Histopathological Assessment of Lung Tissue in Wistar Rats with Pneumonia Induced by Staphylococcus aureus

Histopathological Assessment of Lung Tissue in Wistar Rats with Pneumonia Induced by Staphylococcus aureus | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Histopathological Assessment of Lung Tissue in Wistar Rats with Pneumonia Induced by Staphylococcus aureus Oghenemaro Felix Enwa, Kingsley Chukwuka Amaihunwa, Aya-Ebi Okubo Eneni, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6857728/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background Staphylococcus aureus is a commensal bacterium capable of transitioning into a pathogenic form under favorable conditions, resulting in a wide spectrum of infections. It accounts for approximately 20–50% of hospital-acquired pneumonia (HAP) cases and 25.5% of community-acquired pneumonia (CAP), both of which are associated with substantial morbidity and mortality. The ability of S. aureus to cause severe respiratory illness is of increasing clinical concern, particularly in settings with limited diagnostic and therapeutic resources. Objective This study aimed to evaluate the histopathological alterations in lung tissues of Wistar rats experimentally infected with S. aureus strains isolated from pneumonia patients, and to assess the severity of infection associated with different strains. Methods A total of 1,500 sputum samples were collected from pneumonia patients in randomly selected hospitals across Nigeria. Standard microbiological techniques were employed for the isolation and identification of S. aureus , yielding 79 positive isolates. These isolates were subcultured and used to inoculate healthy Wistar rats intranasally. After a 14-day incubation period, the rats were euthanized, and lung tissues were excised and processed for histological examination using hematoxylin and eosin (H&E) staining. Results Histopathological analysis revealed pronounced pulmonary lesions, including alveolar congestion, infiltration of inflammatory cells, thickening of alveolar septa, and accumulation of exudates and purulent material. Some strains—CU82, CA26, CSA24, CU14, CA43, and CA58—exhibited enhanced virulence, causing more severe tissue destruction. Conclusion This study demonstrates the substantial histopathological damage caused by S. aureus -induced pneumonia and underscores the importance of strain-specific virulence in disease severity. The findings may inform clinical approaches to the diagnosis and management of S. aureus -related pneumonia. Staphylococcus aureus Lung inflammation Virulence factors Respiratory infection Bacterial pneumonia Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 INTRODUCTION A major cause of morbidity and mortality on a global scale, pneumonia is a serious health concern (Collaborators, 2017 ). Because it can cause severe pneumonia and is resistant to standard treatments, Staphylococcus aureus (S. aureus) stands out as a formidable pathogen among the many other pathogens that contribute to this condition (Benhamou et al., 2005 ). About 2–16% of cases of community-acquired pneumonia (CAP) and 20–40% of hospital-acquired pneumonia (HAP) are caused by S. aureus, making it a major etiological pathogen in both conditions (Cilloniz et al., 2017 : Jain et al., 2015 : Stets et al., 2019 ). Pneumonia caused by S. aureus is associated with higher rates of morbidity and mortality compared to other bacterial etiologies, demanding urgent attention from healthcare providers and researchers. Prior investigations have revealed that S. aureus associated mortality in nosocomial pneumonia is approximately 30–50% (Tadros et al., 2013 : Collaborators, 2017 ). In contrast, CAP stemming from S. aureus is associated with mortality rates ranging from 20–50% (Shorr et al., 2010 : Tadros et al., 2013 ), with potential escalation up to 56% in cases of necrotizing pneumonia linked to Panton-Valentine leukocidin (PVL) producing S. aureus strains (Gillet et al ., 2017). Mortality rates from S. aureus pneumonia are three to four times higher than those from Streptococcus pneumoniae, the causative pathogen (Cilloniz et al ., 2021). Its high virulence factor and a variety of antibiotic resistance pathways are responsible for this increased pathogenicity, which leads to powerful multidrug-resistant bacterial infections that pose a serious obstacle to treatment. One of the most significant harmful bacteria is Staphylococcus aureus, which can lead to invasive infectious disorders such as pneumonia, osteomyelitis, septic arthritis, and endocarditis, as well as infections of the skin and soft tissues (Oliveira et al., 2018 ). 20–50% and 25.5% of iatrogenic and community-acquired pneumonia, respectively, are caused by S. aureus and can result in a serious intrapulmonary infection with a high rate of morbidity and mortality. A common drug-resistant bacterium that is thought to be the cause of infections acquired in hospitals and the community is methicillin-resistant S. aureus (MRSA) (Aires-de-Sousa, 2017 ). When the mucosal lining is damaged by viral infections like influenza and measles or by the insertion of an endotracheal tube for mechanical ventilation, the bacteria can enter the upper airway and cause Staphylococcus aureus-induced pneumonia (SAP) (MédecinsSansFrontières, 2020). The host's proinflammatory innate immune response is subsequently triggered by this exposure, resulting in the migration of neutrophils and macrophages as well as the activation of immune cells. By generating inflammation and lung epithelial cell necrosis, the enhanced neutrophil influx into the lungs and the granular toxins they produce contribute to pulmonary disease during SAP (Shambat et al., 2015 ). S. aureus is a remarkably adaptable pathogen that may cause a wide range of illnesses, because of its many virulence factors. Clinical isolates can differ significantly in the expression of their virulence factor genes. In the pathophysiology of pneumonia, not a single S. aureus virulence factor could be identified as being responsible. However, some bacterial toxins, including phenol-soluble modulins (PSMs) (Bloes et al., 2017 ), leucocidins (e.g., Panton–Valentine leukocidin (PVL)) (Diep et al., 2010 ), and pore-forming haemolysin (Hla) (Berube, 2013 ), have been linked to lung infections. The clinical picture of acute pneumonia can be explained by toxins, which are primarily linked to inflammation, tissue degradation, and the production of cell death. Nonetheless, tissue destruction is most likely the consequence of numerous toxic mechanisms because the majority of S. aureus isolates express multiple toxins that interact in a complex manner (Tam and Torres, 2019 ) (Grumann et al., 2013 ). The adhesin class, which includes the fibronectin-binding proteins (FnBPs), is another set of virulence factors that aid in the development of infection (Foster, 2016 ). The components of the staphylococcal surface called adhesins allow the bacterium to cling firmly to the host cells and extracellular matrix. Bacterial uptake can follow adherence to host cells. S. aureus has gained more recognition as an intracellular pathogen that causes a variety of tissue infections during the past ten years (Fraunholz and Sinha, 2020 ). Given the rise in pneumonia cases in recent years, it is imperative to assess the aetiology of the illness as well as its impact on the body's vital organs, as this information may enhance treatment and therapeutic results and lower the death rate. This study is valuable in determining whether Staphylococcus aureus is an organism that causes pneumonia. It is also crucial because it will advance our understanding of how Staphylococcus aureus causes pneumonia and assess the extent of the infection's damage to the lung tissues. MATERIALS AND METHOD COLLECTION OF SAMPLES With the help of the medical laboratory scientists, 1500 sputum samples were collected from clinically diagnosed pneumonia patients in Central Hospital, Benin, Central Hospital, Asaba, University of Benin Teaching hospital (UBTH), Central Hospital, Yenagoa, Stella Obasanjo Women and Children hospital, Benin, Central Hospital, Otuoke, Central Hospital, Warri, Central Hospital, Sapele, Irrua Teaching Hospital. The patients were asked to deposit sputum into sterile universal bottles, the samples were cultured using selective medium for Staphylococci (mannitol salt agar was used), the presence of yellow colonies after culturing confirmed Staphylococcus aureus and seventy-six(76) out of the 1500 samples collected yielded Staphylococcus aureus. 2.3.1 SAMPLE CODES The samples collected were given various codes for easy identification in respect to the hospital location. The various sample codes used for this study include; YEN 10, YEN54, YEN 41, YEN 70, YEN 71, SOH 85, SOH 52,SOH 86, CO 73, OT 45, OT 87, OT 14, OT 53, OT 93 OT 68, OT 2, CS 41, CS 29, CS 53, CS 80,SAP 41, SAP 83, SAP 90,UBT 6, UBT 21, UBT 35, UBT 36, UBT 46, UBT 57, UBT 67, UBT 72, UBT 76, OGH 12, OGH 13, OGH 28, OGH 47, OGH 66, OGH 82, OGH 92, CW 9, CW 47, CW 49, CW 91, CO 5, CO 22, CB 21, CB 91, CB 4, CB 56, CB 88, CY 69, CY 8, CY 44, CY 31, CA 58, ASB 5, ASB 60, ASB 32, ASB 19, ASB 85, ASB 44, CSA 24, CSA 49, CSA 65, CU 14, CU 31, CU 42, CU 70, CU 82, CA 43, CA 20, CA 58, CA 79, SAP 82. 2.4 APPROVAL Ethical approval was granted by the appropriate regulatory body and Ethics committee of the above named hospitals before the samples were collected from diagnosed patients. 2.5 PREPARATION OF MEDIA AND SUB CULTURING 1.3g of nutrient agar was weighed and dissolved in 100mls of distilled water, 4mls of the broth was dispensed into already washed McCartney bottles and the nutrient broth was sterilized in an autoclave at 121 0 C for 15 minutes. After sterilizing, it was allowed to cool and labeled using the various codes for the samples. The broth medium was inoculated with the various samples of Staphylococcus aureus and was incubated at 37 o C for 24 hours. After sub culturing, 76 Wistar rats were weighed individually, they were given specific markings for easy identification after which they were induced with the sub cultured Staphylococcus aureus inducing pneumonia by injecting with 1ml intraperitoneally. The subjects were kept for 14 days with adequate feeding and proper monitoring. 2.6 TISSUE HARVESTING The induced rats were sacrificed after 14 days following injection, the blood samples were collected via the retro orbital plexus into EDTA bottles and lithium heparin for individual animals, then dissected and the lungs were harvested and placed in labeled universal bottles containing formal saline to preserve it and the lung was submerged in the formal saline. The harvested lungs were taken to the laboratory for histological analysis. Tissue processing and staining procedure were carried out as described by Awvioro 2002 PHOTOMICROGRAPHY The stained tissue images were captured using a digital microscopic eyepiece. RESULTS The laboratory result after testing presented with several effect, deformities and pathological changes which is been manifested physiologically. These effects varied with the different strains of the organism obtained from different location wherein the study was carried out. Effect of staphylococcus aureus inducing pneumonia is dependent on the virulence of the strain of the organism. After laboratory examinations of infected laboratory animals, similar examination was carried out on a healthy non infected animal tissue (lungs) and this served as a test control (standard) to other lung tissues examined. The control sample presented the histology and physiology of healthy lungs and was used to evaluate the histological presentation of other lung tissues been infected with staphylococcus aureus inducing pneumonia. Photomicrograph shows section of the lung tissue consisting the alveoli (A) lined type I pnuemocytes (arrow), type ii pnuemocytes (arrow head), the blood capillaries (C) lies within the Interstitium. Section free from congestion and inflammatory cells. HISTOLOGICAL PRESENTATION OF INFECTED LUNGS TISSUE DISCUSSION The lungs, as the primary organs of the human respiratory system, play a critical role in maintaining respiratory health and overall quality of life. Due to their anatomical exposure to the external environment, lungs are particularly susceptible to infections and environmental insults (Vieira et al., 2019). Among respiratory infections, the lungs serve as the primary site for co-infections involving influenza viruses and bacterial pathogens, where the innate immune system is rapidly activated to facilitate pathogen clearance and promote host survival. However, pathogenic bacteria such as Staphylococcus aureus have evolved sophisticated survival mechanisms that allow them to evade immune responses. Notably, recent research has shown that S. aureus can persist intracellularly within non-phagocytic cells, including epithelial and endothelial cells, adopting a dormant state and awaiting favorable conditions for proliferation (Leidecker et al., 2023 ; Niemann et al., 2021 ). Historically, Staphylococcus aureus pneumonia was considered rare, with Streptococcus pneumoniae being the predominant etiological agent of community-acquired pneumonia (CAP). However, a growing body of evidence suggests a rising incidence of S. aureus -associated pneumonia, particularly in both community-acquired and nosocomial settings. In this study, microbiological analysis and differential staining of samples collected from clinically diagnosed pneumonia patients revealed that S. aureus was responsible for 18.9% of the cases, indicating a significant presence. Previous studies have reported mortality rates ranging from 30–50% for nosocomial pneumonia caused by S. aureus (Tadros et al., 2013 ; Collaborators, 2017 ), while community-acquired S. aureus pneumonia (CAP-SA) has shown fatality rates between 20% and 50% (Shorr et al., 2010 ; Tadros et al., 2013 ). In this investigation, out of 1,500 clinical samples processed, 76 isolates were confirmed as S. aureus via culturing on Mannitol Salt Agar. Pathological examination of these isolates indicated that the severity of pulmonary infection varied among the strains. This aligns with findings by Diep et al. ( 2010 ), who demonstrated that Panton-Valentine leukocidin (PVL), a bicomponent toxin produced by S. aureus , contributes to pulmonary tissue damage by lysing polymorphonuclear leukocytes. Despite this, most S. aureus pneumonia cases have been associated with PVL-negative strains, suggesting that other virulence factors significantly contribute to pathogenesis. Histopathological analysis of lung tissues in this study revealed marked inflammatory responses characterized by immune cell infiltration—hallmarks of bacterial pneumonia and acute lung injury (Goodman et al., 2003 ). Evidence of vascular congestion and hemorrhagic lesions, marked by red patches, was indicative of protease Spl activity—a protease unique to S. aureus associated with pulmonary hemorrhage (Paharik et al., 2016 ). Furthermore, signs of alveolar epithelial degeneration, including cellular blebbing, nuclear fragmentation, and chromatin condensation, suggest apoptotic processes consistent with descriptions by Lam et al. (2016). Additional features such as necrosis, alveolar consolidation, and architectural distortion of the lung parenchyma further affirm the destructive potential of S. aureus infection (Berube & Bubeck, 2013). In contrast, lung tissues from the control group showed no histopathological abnormalities, underscoring the direct impact of S. aureus virulence. The severity of inflammation and tissue damage varied across isolates, with some strains—specifically CU82, CA26, CSA24, CU14, CA43, and CA58—inducing more extensive pathology. This variability is likely attributable to the differential expression of virulence determinants encoded in the accessory genome of S. aureus . While the core genome houses essential housekeeping genes, the accessory genome comprises mobile genetic elements (MGEs) such as plasmids, transposons, prophages, and pathogenicity islands, which encode numerous virulence and antibiotic resistance factors (Lindsay, 2019). Virulence genes located on prophages include PVL, the chemotaxis inhibitory protein (CHIPS), staphylococcal complement inhibitor (SCIN), exfoliative toxins A and B, staphylokinase, and various enterotoxins (Malachowa & DeLeo, 2010). Meanwhile, antibiotic resistance genes are typically associated with plasmids and transposons. The diversity and composition of these MGEs likely contribute to the observed strain-dependent pathogenicity and clinical outcomes in S. aureus -induced pneumonia. CONCLUSION This study provided a histopathological evaluation of the pulmonary tissues of Wistar rats experimentally infected with Staphylococcus aureus isolates, confirming the organism’s potential to induce pneumonia. The isolates were recovered using selective media specific for S. aureus and subsequently used to infect animal models to assess the severity and extent of lung damage. Following infection, histological examinations revealed varying degrees of tissue inflammation, alveolar consolidation, and structural disintegration across the different bacterial strains. The findings demonstrate that S. aureus, in addition to Streptococcus pneumoniae, is a significant etiological agent of pneumonia, capable of causing severe respiratory complications. This underscores the clinical importance of considering S. aureus in differential diagnoses of pneumonia, especially in cases unresponsive to conventional therapy. Furthermore, the variability in virulence among the strains highlights the complexity of host-pathogen interactions and the need for tailored therapeutic strategies. The study also emphasizes the growing concern of antibiotic resistance in S. aureus, which complicates treatment and increases the risk of adverse clinical outcomes. The observed pulmonary damage in infected models suggests that S. aureus-induced pneumonia can result in significant respiratory impairment, contributing to reduced quality of life and potential mortality if not promptly and effectively managed. In conclusion, the study reinforces the pathogenic role of S. aureus in pneumonia, the associated histopathological changes in lung tissue, and the pressing need for improved diagnostic, preventive, and therapeutic measures to manage S. aureus-related respiratory infections. RECOMMENDATIONS Based on the findings of this study, the following recommendations are proposed to enhance the diagnosis, treatment, and prevention of Staphylococcus aureus -induced pneumonia: Comprehensive microbiological diagnosis should be routinely conducted for patients presenting with pneumonia symptoms to accurately identify the causative organism and inform appropriate therapeutic strategies. Early clinical intervention is critical for individuals exhibiting signs of pneumonia to prevent disease progression and irreversible pulmonary damage. Strict hygiene practices should be enforced in both community and healthcare settings, given the increasing incidence of S. aureus -associated pneumonia. Public health campaigns and educational programs should be initiated by government bodies, healthcare institutions, and research organizations to raise awareness about the risks, symptoms, and prevention of Staphylococcus aureus pneumonia. The use of combination antimicrobial therapies is strongly recommended to mitigate the emergence of antibiotic resistance commonly associated with S. aureus . Ongoing research and drug development efforts are essential to produce novel, more potent antibiotics capable of effectively treating resistant strains of S. aureus . Declarations Author Contribution OO, OCS and KCA wrote the main manuscript text. AOE, OFE and FA prepared all the figures. All authors reviewed the manuscript. Contribution to Knowledge This study confirms that pneumonia is not solely caused by Streptococcus pneumoniae , but also significantly by Staphylococcus aureus . It demonstrates that S. aureus -induced pneumonia can lead to extensive histopathological damage in the lungs, emphasizing its clinical severity. It further establishes Staphylococcus aureus as one of the most virulent species within the genus Staphylococcus , with a high potential for antibiotic resistance and severe respiratory implications. 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Staphylococcus aureus secreted toxins and extracellular enzymes. Microbiology Spectrum, 7 (2). https://doi.org/10.1128/microbiolspec.GPP3-0039-2018 Ventura, C. L., Higdon, R., Hohmann, L., Martin, D., Kolker, E., Liggitt, H. D., Skerrett, S. J., & Rubens, C. E. (2008). Staphylococcus aureus elicits marked alterations in the airway proteome during early pneumonia. Infection and Immunity, 76 (12), 5862–5872. https://doi.org/10.1128/IAI.00671-08 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6857728","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":472747642,"identity":"4b8e7af5-dd2d-4f1c-94e0-6545a65fa02d","order_by":0,"name":"Oghenemaro Felix Enwa","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+UlEQVRIiWNgGAWjYBAC9gbmhgNQlgHDAzArAb8WngOMUC08BwygionQAmFJJBCrhb2x8TBPxZ3E/pmPNz5I+HOYgZ89x4C54BceLTwHGw7OOPMsccbttGKDxLbDDJI9bwyYZ/bh1mIvkdhw4GPb4dyG2zlmQPZhBoMbQFt4e/DYIv+w4UDiv8O582+eMf8Bcpg9QS0SwBD72HA4d8MNHjOGBDagLRJALTw/8PklEeiXY4frN55JK5ZIbEvnkTjzrOAwbwMeLeyHD3/mqTlsLHf88MYPH/5Yy/G3J298zPMHtxZMM0DEAcY2ErRAASm2jIJRMApGwXAHAMTdXOkulcVvAAAAAElFTkSuQmCC","orcid":"","institution":"Delta State University Abraka","correspondingAuthor":true,"prefix":"","firstName":"Oghenemaro","middleName":"Felix","lastName":"Enwa","suffix":""},{"id":472747644,"identity":"c26613dc-6d6a-47ec-801e-cc33cf28b87d","order_by":1,"name":"Kingsley Chukwuka Amaihunwa","email":"","orcid":"","institution":"Delta State University Abraka","correspondingAuthor":false,"prefix":"","firstName":"Kingsley","middleName":"Chukwuka","lastName":"Amaihunwa","suffix":""},{"id":472747648,"identity":"cd9796db-a673-45f4-b144-350345d065a7","order_by":2,"name":"Aya-Ebi Okubo Eneni","email":"","orcid":"","institution":"Delta State University Abraka","correspondingAuthor":false,"prefix":"","firstName":"Aya-Ebi","middleName":"Okubo","lastName":"Eneni","suffix":""},{"id":472747649,"identity":"7c97ec1c-3503-47ae-aa7f-2fb587efa45d","order_by":3,"name":"Onome Cyril Sadjere","email":"","orcid":"","institution":"Delta State University Abraka","correspondingAuthor":false,"prefix":"","firstName":"Onome","middleName":"Cyril","lastName":"Sadjere","suffix":""},{"id":472747652,"identity":"f102af5c-0349-4e94-aa5a-b3f63ee2b8c3","order_by":4,"name":"Faith Akpakpan","email":"","orcid":"","institution":"Delta State University Abraka","correspondingAuthor":false,"prefix":"","firstName":"Faith","middleName":"","lastName":"Akpakpan","suffix":""},{"id":472747653,"identity":"6c79f6ea-f863-46ec-aa30-bbe0bd2c33c0","order_by":5,"name":"Osawan Okunbor","email":"","orcid":"","institution":"Delta State University Abraka","correspondingAuthor":false,"prefix":"","firstName":"Osawan","middleName":"","lastName":"Okunbor","suffix":""}],"badges":[],"createdAt":"2025-06-09 23:53:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6857728/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6857728/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85181267,"identity":"433f0002-8cf3-4e11-8849-70f148f003d3","added_by":"auto","created_at":"2025-06-23 07:23:34","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":249845,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlide 3.1 \u003c/strong\u003egives the histological presentation of the test control\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eControl 3 X400HE TECHNIQUE\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePhotomicrograph shows section of the lung tissue consisting the alveoli (A) lined type I pnuemocytes (arrow), type ii pnuemocytes (arrow head), the blood capillaries (C) lies within the Interstitium. Section free from congestion and inflammatory cells.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/80b12975aa3b3b9a1f970abb.png"},{"id":85180487,"identity":"46c26a8d-c705-406e-a523-7707223f7166","added_by":"auto","created_at":"2025-06-23 07:15:34","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":213088,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlide 3.2.1. CA 26 X400 HE TECHNIQUE\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhotomicrograph shows section of the lungs with marked interstitial inflammatory cells infiltrates (Circle) and vascular congestion (star).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/a134aec5ca74140a087acb67.png"},{"id":85180486,"identity":"24e62d18-81d9-4c2d-b44b-1f4e41c8de60","added_by":"auto","created_at":"2025-06-23 07:15:34","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":252164,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlide 3.2.2. CA 43 X400 HE TECHNIQUE\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhotomicrograph shows section of the lungs with marked perivascular inflammatory cells infiltrates (Circle) and vascular congestion (star).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/ba809e26831440836eb722ae.png"},{"id":85180494,"identity":"3e51e78a-ce48-4241-8c66-28c7ebe036f9","added_by":"auto","created_at":"2025-06-23 07:15:34","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":214883,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlide 3.2.3. CA 58 X400 HE TECHNIQUE\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhotomicrograph shows section of the lungs with vascular congestion (VS), perivascular inflammatory cells infiltrates and peribronchial infiltrates (arrow).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/b9f2f5ab55d7c88108461555.png"},{"id":85180492,"identity":"e24bcc45-65f0-4a72-a073-3824a6a51aa8","added_by":"auto","created_at":"2025-06-23 07:15:34","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":212243,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlide 3.2.4 CA 79 X400 HE TECHNIQUE\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhotomicrograph shows section of the lungs with vascular congestion (VS) and interstitial inflammatory cells infiltrates.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/4622e9c8ad077276c95dda3a.png"},{"id":85180504,"identity":"79a3fe0a-a8d8-4a71-b5c6-820eb8ee67e0","added_by":"auto","created_at":"2025-06-23 07:15:34","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":225725,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlide 3.2.5 CSA 24 X400 HE TECHNIQUE\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSection shows vascular congestion (Star), asymmetrical vascular medial hypertrophy (Line) and perivascular inflammatory cells infiltrations.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/7fdd1e61e742a6be3c0f4545.png"},{"id":85181977,"identity":"b309be69-b5de-43c5-8f83-0ebd18c6de16","added_by":"auto","created_at":"2025-06-23 07:31:34","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":302274,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlide 3.2.6 CSA 65 \u0026nbsp;X400 HE TECHNIQUE\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhotomicrograph shows marked interstitial lymphoid aggregates (star).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/c257a8d7086887a6c444d704.png"},{"id":85180498,"identity":"2d29227b-d492-43a0-b7cb-bd8e70a77740","added_by":"auto","created_at":"2025-06-23 07:15:34","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":239800,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlide 3.2.7 CU 14 X400 HE TECHNIQUE\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhotomicrograph shows section of the lungs with marked perivascular inflammatory cells infiltrates (Circle) and vascular congestion (star).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/bb142a16e659b6c6a624ef9c.png"},{"id":85181981,"identity":"38281956-8ef8-4c90-9885-fad6be9f134e","added_by":"auto","created_at":"2025-06-23 07:31:35","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":307111,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlide 3.2.8 CU 31 X400HE TECHNIQUE\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhotomicrograph shows section of the lungs with marked perivascular inflammatory cells infiltrates (Circle) and vascular congestion (star).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/0714733c4c91c708ad8dc7ad.png"},{"id":85180509,"identity":"73b800d5-9fc9-4e7e-8ae3-5f41c3b3f6d4","added_by":"auto","created_at":"2025-06-23 07:15:35","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":313868,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlide 3.2.9 CU 42 X400 HE TECHNIQUE\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhotomicrograph shows section of the lungs with marked vascular congestion (vc) and interstitial inflammatory cells aggregations (arrow).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/1f32a15b1564bb85d3cb69b1.png"},{"id":85180500,"identity":"cd8f12fe-874b-48fc-b5cd-40eb14e09ab5","added_by":"auto","created_at":"2025-06-23 07:15:34","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":228541,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlide 3.2.10 CU 70 X400 HE TECHNIQUE\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhotomicrograph shows marked interstitial congestion (star) and interstitial inflammatory cells.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/6510befa7365ddc4c3c069b0.png"},{"id":85181276,"identity":"584f4290-c463-4983-b0b8-7c92b0c53fe2","added_by":"auto","created_at":"2025-06-23 07:23:35","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":212420,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlide 3.2.11 CU 82X400HE TECHNIQUE\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhotomicrograph shows section of the lungs with marked perivascular inflammatory cells infiltrates (Circle) and vascular congestion (star).TB terminal bronchiole.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage12.png","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/58724d7c7ba2b84429769e92.png"},{"id":109907668,"identity":"800df62a-dac3-48fa-b483-0ca509ffad56","added_by":"auto","created_at":"2026-05-25 06:42:48","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3195147,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6857728/v1/24977f28-6e17-45df-80f0-aadbd8ba90fa.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eHistopathological Assessment of Lung Tissue in Wistar Rats with Pneumonia Induced by \u003cem\u003eStaphylococcus aureus\u003c/em\u003e\u003c/p\u003e","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eA major cause of morbidity and mortality on a global scale, pneumonia is a serious health concern (Collaborators, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Because it can cause severe pneumonia and is resistant to standard treatments, Staphylococcus aureus (S. aureus) stands out as a formidable pathogen among the many other pathogens that contribute to this condition (Benhamou et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). About 2\u0026ndash;16% of cases of community-acquired pneumonia (CAP) and 20\u0026ndash;40% of hospital-acquired pneumonia (HAP) are caused by S. aureus, making it a major etiological pathogen in both conditions (Cilloniz et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2017\u003c/span\u003e: Jain et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2015\u003c/span\u003e: Stets et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Pneumonia caused by S. aureus is associated with higher rates of morbidity and mortality compared to other bacterial etiologies, demanding urgent attention from healthcare providers and researchers. Prior investigations have revealed that S. aureus associated mortality in nosocomial pneumonia is approximately 30\u0026ndash;50% (Tadros et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2013\u003c/span\u003e: Collaborators, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In contrast, CAP stemming from S. aureus is associated with mortality rates ranging from 20\u0026ndash;50% (Shorr et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2010\u003c/span\u003e: Tadros et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), with potential escalation up to 56% in cases of necrotizing pneumonia linked to Panton-Valentine leukocidin (PVL) producing S. aureus strains (Gillet \u003cem\u003eet al\u003c/em\u003e., 2017). Mortality rates from S. aureus pneumonia are three to four times higher than those from Streptococcus pneumoniae, the causative pathogen (Cilloniz \u003cem\u003eet al\u003c/em\u003e., 2021). Its high virulence factor and a variety of antibiotic resistance pathways are responsible for this increased pathogenicity, which leads to powerful multidrug-resistant bacterial infections that pose a serious obstacle to treatment.\u003c/p\u003e \u003cp\u003eOne of the most significant harmful bacteria is Staphylococcus aureus, which can lead to invasive infectious disorders such as pneumonia, osteomyelitis, septic arthritis, and endocarditis, as well as infections of the skin and soft tissues (Oliveira et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). 20\u0026ndash;50% and 25.5% of iatrogenic and community-acquired pneumonia, respectively, are caused by S. aureus and can result in a serious intrapulmonary infection with a high rate of morbidity and mortality. A common drug-resistant bacterium that is thought to be the cause of infections acquired in hospitals and the community is methicillin-resistant S. aureus (MRSA) (Aires-de-Sousa, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). When the mucosal lining is damaged by viral infections like influenza and measles or by the insertion of an endotracheal tube for mechanical ventilation, the bacteria can enter the upper airway and cause Staphylococcus aureus-induced pneumonia (SAP) (M\u0026eacute;decinsSansFronti\u0026egrave;res, 2020). The host's proinflammatory innate immune response is subsequently triggered by this exposure, resulting in the migration of neutrophils and macrophages as well as the activation of immune cells. By generating inflammation and lung epithelial cell necrosis, the enhanced neutrophil influx into the lungs and the granular toxins they produce contribute to pulmonary disease during SAP (Shambat et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eS. aureus is a remarkably adaptable pathogen that may cause a wide range of illnesses, because of its many virulence factors. Clinical isolates can differ significantly in the expression of their virulence factor genes. In the pathophysiology of pneumonia, not a single S. aureus virulence factor could be identified as being responsible. However, some bacterial toxins, including phenol-soluble modulins (PSMs) (Bloes et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), leucocidins (e.g., Panton\u0026ndash;Valentine leukocidin (PVL)) (Diep et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), and pore-forming haemolysin (Hla) (Berube, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), have been linked to lung infections.\u003c/p\u003e \u003cp\u003eThe clinical picture of acute pneumonia can be explained by toxins, which are primarily linked to inflammation, tissue degradation, and the production of cell death. Nonetheless, tissue destruction is most likely the consequence of numerous toxic mechanisms because the majority of S. aureus isolates express multiple toxins that interact in a complex manner (Tam and Torres, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) (Grumann et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The adhesin class, which includes the fibronectin-binding proteins (FnBPs), is another set of virulence factors that aid in the development of infection (Foster, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The components of the staphylococcal surface called adhesins allow the bacterium to cling firmly to the host cells and extracellular matrix. Bacterial uptake can follow adherence to host cells. S. aureus has gained more recognition as an intracellular pathogen that causes a variety of tissue infections during the past ten years (Fraunholz and Sinha, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eGiven the rise in pneumonia cases in recent years, it is imperative to assess the aetiology of the illness as well as its impact on the body's vital organs, as this information may enhance treatment and therapeutic results and lower the death rate. This study is valuable in determining whether Staphylococcus aureus is an organism that causes pneumonia. It is also crucial because it will advance our understanding of how Staphylococcus aureus causes pneumonia and assess the extent of the infection's damage to the lung tissues.\u003c/p\u003e"},{"header":"MATERIALS AND METHOD","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eCOLLECTION OF SAMPLES\u003c/h2\u003e \u003cp\u003eWith the help of the medical laboratory scientists, 1500 sputum samples were collected from clinically diagnosed pneumonia patients in Central Hospital, Benin, Central Hospital, Asaba, University of Benin Teaching hospital (UBTH), Central Hospital, Yenagoa, Stella Obasanjo Women and Children hospital, Benin, Central Hospital, Otuoke, Central Hospital, Warri, Central Hospital, Sapele, Irrua Teaching Hospital. The patients were asked to deposit sputum into sterile universal bottles, the samples were cultured using selective medium for \u003cem\u003eStaphylococci\u003c/em\u003e (mannitol salt agar was used), the presence of yellow colonies after culturing confirmed \u003cem\u003eStaphylococcus aureus\u003c/em\u003e and seventy-six(76) out of the 1500 samples collected yielded \u003cem\u003eStaphylococcus aureus.\u003c/em\u003e\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e2.3.1 SAMPLE CODES\u003c/h3\u003e\n\u003cp\u003eThe samples collected were given various codes for easy identification in respect to the hospital location. The various sample codes used for this study include; YEN 10, YEN54, YEN 41, YEN 70, YEN 71, SOH 85, SOH 52,SOH 86, CO 73, OT 45, OT 87, OT 14, OT 53, OT 93 OT 68, OT 2, CS 41, CS 29, CS 53, CS 80,SAP 41, SAP 83, SAP 90,UBT 6, UBT 21, UBT 35, UBT 36, UBT 46, UBT 57, UBT 67, UBT 72, UBT 76, OGH 12, OGH 13, OGH 28, OGH 47, OGH 66, OGH 82, OGH 92, CW 9, CW 47, CW 49, CW 91, CO 5, CO 22, CB 21, CB 91, CB 4, CB 56, CB 88, CY 69, CY 8, CY 44, CY 31, CA 58, ASB 5, ASB 60, ASB 32, ASB 19, ASB 85, ASB 44, CSA 24, CSA 49, CSA 65, CU 14, CU 31, CU 42, CU 70, CU 82, CA 43, CA 20, CA 58, CA 79, SAP 82.\u003c/p\u003e\n\u003ch3\u003e2.4 APPROVAL\u003c/h3\u003e\n\u003cp\u003eEthical approval was granted by the appropriate regulatory body and Ethics committee of the above named hospitals before the samples were collected from diagnosed patients.\u003c/p\u003e \u003c/p\u003e\n\u003ch3\u003e2.5 PREPARATION OF MEDIA AND SUB CULTURING\u003c/h3\u003e\n\u003cp\u003e1.3g of nutrient agar was weighed and dissolved in 100mls of distilled water, 4mls of the broth was dispensed into already washed McCartney bottles and the nutrient broth was sterilized in an autoclave at 121\u003csup\u003e0\u003c/sup\u003eC for 15 minutes. After sterilizing, it was allowed to cool and labeled using the various codes for the samples. The broth medium was inoculated with the various samples of \u003cem\u003eStaphylococcus aureus\u003c/em\u003e and was incubated at 37\u003csup\u003eo\u003c/sup\u003eC for 24 hours.\u003c/p\u003e \u003cp\u003eAfter sub culturing, 76 Wistar rats were weighed individually, they were given specific markings for easy identification after which they were induced with the sub cultured \u003cem\u003eStaphylococcus aureus\u003c/em\u003e inducing pneumonia by injecting with 1ml intraperitoneally. The subjects were kept for 14 days with adequate feeding and proper monitoring.\u003c/p\u003e\n\u003ch3\u003e2.6 TISSUE HARVESTING\u003c/h3\u003e\n\u003cp\u003eThe induced rats were sacrificed after 14 days following injection, the blood samples were collected via the retro orbital plexus into EDTA bottles and lithium heparin for individual animals, then dissected and the lungs were harvested and placed in labeled universal bottles containing formal saline to preserve it and the lung was submerged in the formal saline. The harvested lungs were taken to the laboratory for histological analysis. Tissue processing and staining procedure were carried out as described by Awvioro 2002\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003ePHOTOMICROGRAPHY\u003c/h2\u003e \u003cp\u003eThe stained tissue images were captured using a digital microscopic eyepiece.\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS","content":"\u003cp\u003eThe laboratory result after testing presented with several effect, deformities and pathological changes which is been manifested physiologically. These effects varied with the different strains of the organism obtained from different location wherein the study was carried out.\u003c/p\u003e\n\u003cp\u003eEffect of \u003cem\u003estaphylococcus aureus\u003c/em\u003e inducing pneumonia is dependent on the virulence of the strain of the organism. After laboratory examinations of infected laboratory animals, similar examination was carried out on a healthy non infected animal tissue (lungs) and this served as a test control (standard) to other lung tissues examined. The control sample presented the histology and physiology of healthy lungs and was used to evaluate the histological presentation of other lung tissues been infected with \u003cem\u003estaphylococcus aureus\u003c/em\u003e inducing pneumonia.\u003c/p\u003e\n\u003cp\u003ePhotomicrograph shows section of the lung tissue consisting the alveoli (A) lined type I pnuemocytes (arrow), type ii pnuemocytes (arrow head), the blood capillaries (C) lies within the Interstitium. Section free from congestion and inflammatory cells.\u003c/p\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003eHISTOLOGICAL PRESENTATION OF INFECTED LUNGS TISSUE\u003c/h2\u003e\n\u003c/div\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThe lungs, as the primary organs of the human respiratory system, play a critical role in maintaining respiratory health and overall quality of life. Due to their anatomical exposure to the external environment, lungs are particularly susceptible to infections and environmental insults (Vieira et al., 2019). Among respiratory infections, the lungs serve as the primary site for co-infections involving influenza viruses and bacterial pathogens, where the innate immune system is rapidly activated to facilitate pathogen clearance and promote host survival. However, pathogenic bacteria such as \u003cem\u003eStaphylococcus aureus\u003c/em\u003e have evolved sophisticated survival mechanisms that allow them to evade immune responses. Notably, recent research has shown that \u003cem\u003eS. aureus\u003c/em\u003e can persist intracellularly within non-phagocytic cells, including epithelial and endothelial cells, adopting a dormant state and awaiting favorable conditions for proliferation (Leidecker et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Niemann et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHistorically, \u003cem\u003eStaphylococcus aureus\u003c/em\u003e pneumonia was considered rare, with \u003cem\u003eStreptococcus pneumoniae\u003c/em\u003e being the predominant etiological agent of community-acquired pneumonia (CAP). However, a growing body of evidence suggests a rising incidence of \u003cem\u003eS. aureus\u003c/em\u003e-associated pneumonia, particularly in both community-acquired and nosocomial settings. In this study, microbiological analysis and differential staining of samples collected from clinically diagnosed pneumonia patients revealed that \u003cem\u003eS. aureus\u003c/em\u003e was responsible for 18.9% of the cases, indicating a significant presence. Previous studies have reported mortality rates ranging from 30\u0026ndash;50% for nosocomial pneumonia caused by \u003cem\u003eS. aureus\u003c/em\u003e (Tadros et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Collaborators, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), while community-acquired \u003cem\u003eS. aureus\u003c/em\u003e pneumonia (CAP-SA) has shown fatality rates between 20% and 50% (Shorr et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Tadros et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn this investigation, out of 1,500 clinical samples processed, 76 isolates were confirmed as \u003cem\u003eS. aureus\u003c/em\u003e via culturing on Mannitol Salt Agar. Pathological examination of these isolates indicated that the severity of pulmonary infection varied among the strains. This aligns with findings by Diep et al. (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), who demonstrated that Panton-Valentine leukocidin (PVL), a bicomponent toxin produced by \u003cem\u003eS. aureus\u003c/em\u003e, contributes to pulmonary tissue damage by lysing polymorphonuclear leukocytes. Despite this, most \u003cem\u003eS. aureus\u003c/em\u003e pneumonia cases have been associated with PVL-negative strains, suggesting that other virulence factors significantly contribute to pathogenesis.\u003c/p\u003e \u003cp\u003eHistopathological analysis of lung tissues in this study revealed marked inflammatory responses characterized by immune cell infiltration\u0026mdash;hallmarks of bacterial pneumonia and acute lung injury (Goodman et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Evidence of vascular congestion and hemorrhagic lesions, marked by red patches, was indicative of protease Spl activity\u0026mdash;a protease unique to \u003cem\u003eS. aureus\u003c/em\u003e associated with pulmonary hemorrhage (Paharik et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Furthermore, signs of alveolar epithelial degeneration, including cellular blebbing, nuclear fragmentation, and chromatin condensation, suggest apoptotic processes consistent with descriptions by Lam et al. (2016). Additional features such as necrosis, alveolar consolidation, and architectural distortion of the lung parenchyma further affirm the destructive potential of \u003cem\u003eS. aureus\u003c/em\u003e infection (Berube \u0026amp; Bubeck, 2013).\u003c/p\u003e \u003cp\u003eIn contrast, lung tissues from the control group showed no histopathological abnormalities, underscoring the direct impact of \u003cem\u003eS. aureus\u003c/em\u003e virulence. The severity of inflammation and tissue damage varied across isolates, with some strains\u0026mdash;specifically CU82, CA26, CSA24, CU14, CA43, and CA58\u0026mdash;inducing more extensive pathology. This variability is likely attributable to the differential expression of virulence determinants encoded in the accessory genome of \u003cem\u003eS. aureus\u003c/em\u003e. While the core genome houses essential housekeeping genes, the accessory genome comprises mobile genetic elements (MGEs) such as plasmids, transposons, prophages, and pathogenicity islands, which encode numerous virulence and antibiotic resistance factors (Lindsay, 2019).\u003c/p\u003e \u003cp\u003eVirulence genes located on prophages include PVL, the chemotaxis inhibitory protein (CHIPS), staphylococcal complement inhibitor (SCIN), exfoliative toxins A and B, staphylokinase, and various enterotoxins (Malachowa \u0026amp; DeLeo, 2010). Meanwhile, antibiotic resistance genes are typically associated with plasmids and transposons. The diversity and composition of these MGEs likely contribute to the observed strain-dependent pathogenicity and clinical outcomes in \u003cem\u003eS. aureus\u003c/em\u003e-induced pneumonia.\u003c/p\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003eThis study provided a histopathological evaluation of the pulmonary tissues of Wistar rats experimentally infected with Staphylococcus aureus isolates, confirming the organism\u0026rsquo;s potential to induce pneumonia. The isolates were recovered using selective media specific for S. aureus and subsequently used to infect animal models to assess the severity and extent of lung damage. Following infection, histological examinations revealed varying degrees of tissue inflammation, alveolar consolidation, and structural disintegration across the different bacterial strains.\u003c/p\u003e \u003cp\u003eThe findings demonstrate that S. aureus, in addition to Streptococcus pneumoniae, is a significant etiological agent of pneumonia, capable of causing severe respiratory complications. This underscores the clinical importance of considering S. aureus in differential diagnoses of pneumonia, especially in cases unresponsive to conventional therapy. Furthermore, the variability in virulence among the strains highlights the complexity of host-pathogen interactions and the need for tailored therapeutic strategies.\u003c/p\u003e \u003cp\u003eThe study also emphasizes the growing concern of antibiotic resistance in S. aureus, which complicates treatment and increases the risk of adverse clinical outcomes. The observed pulmonary damage in infected models suggests that S. aureus-induced pneumonia can result in significant respiratory impairment, contributing to reduced quality of life and potential mortality if not promptly and effectively managed.\u003c/p\u003e \u003cp\u003eIn conclusion, the study reinforces the pathogenic role of S. aureus in pneumonia, the associated histopathological changes in lung tissue, and the pressing need for improved diagnostic, preventive, and therapeutic measures to manage S. aureus-related respiratory infections.\u003c/p\u003e \u003cdiv id=\"Sec33\" class=\"Section2\"\u003e \u003ch2\u003eRECOMMENDATIONS\u003c/h2\u003e \u003cp\u003eBased on the findings of this study, the following recommendations are proposed to enhance the diagnosis, treatment, and prevention of \u003cem\u003eStaphylococcus aureus\u003c/em\u003e-induced pneumonia:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eComprehensive microbiological diagnosis should be routinely conducted for patients presenting with pneumonia symptoms to accurately identify the causative organism and inform appropriate therapeutic strategies.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eEarly clinical intervention is critical for individuals exhibiting signs of pneumonia to prevent disease progression and irreversible pulmonary damage.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eStrict hygiene practices should be enforced in both community and healthcare settings, given the increasing incidence of \u003cem\u003eS. aureus\u003c/em\u003e-associated pneumonia.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003ePublic health campaigns and educational programs should be initiated by government bodies, healthcare institutions, and research organizations to raise awareness about the risks, symptoms, and prevention of \u003cem\u003eStaphylococcus aureus\u003c/em\u003e pneumonia.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe use of combination antimicrobial therapies is strongly recommended to mitigate the emergence of antibiotic resistance commonly associated with \u003cem\u003eS. aureus\u003c/em\u003e.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eOngoing research and drug development efforts are essential to produce novel, more potent antibiotics capable of effectively treating resistant strains of \u003cem\u003eS. aureus\u003c/em\u003e.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003c/div\u003e "},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eOO, OCS and KCA wrote the main manuscript text. AOE, OFE and FA prepared all the figures. All authors reviewed the manuscript.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eContribution to Knowledge\u003c/strong\u003e\u003c/p\u003e\n\u003cul type=\"disc\"\u003e\n \u003cli\u003eThis study confirms that pneumonia is not solely caused by \u003cem\u003eStreptococcus pneumoniae\u003c/em\u003e, but also significantly by \u003cem\u003eStaphylococcus aureus\u003c/em\u003e.\u003c/li\u003e\n \u003cli\u003eIt demonstrates that \u003cem\u003eS. aureus\u003c/em\u003e-induced pneumonia can lead to extensive histopathological damage in the lungs, emphasizing its clinical severity.\u003c/li\u003e\n \u003cli\u003eIt further establishes \u003cem\u003eStaphylococcus aureus\u003c/em\u003e as one of the most virulent species within the genus \u003cem\u003eStaphylococcus\u003c/em\u003e, with a high potential for antibiotic resistance and severe respiratory implications.\u003c/li\u003e\n\u003c/ul\u003e\n"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAires-de-Sousa, M. (2017). 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M. (2013). \u003cem\u003eStaphylococcus aureus\u003c/em\u003e toxins\u0026mdash;Their functions and genetics. In \u003cem\u003eRobert Koch-Institut\u003c/em\u003e (Vol. 21, pp. 583\u0026ndash;592).\u003c/li\u003e\n\u003cli\u003eJain, S., Self, W. H., Wunderink, R. G., Fakhran, S., Balk, R., Bramley, A. M., \u0026amp; Waterer, G. W. (2015). Community-acquired pneumonia requiring hospitalization among U.S. adults. \u003cem\u003eNew England Journal of Medicine, 373\u003c/em\u003e(5), 415\u0026ndash;427. https://doi.org/10.1056/NEJMoa1500245\u003c/li\u003e\n\u003cli\u003eLeidecker, M., Bertling, A., Hussain, M., \u0026amp; Peters, G. (2023). Protein disulfide isomerase and extracellular adherence protein cooperatively potentiate staphylococcal invasion into endothelial cells. \u003cem\u003eMicrobiology Spectrum, 11\u003c/em\u003e(3), e03886-22. https://doi.org/10.1128/spectrum.03886-22\u003c/li\u003e\n\u003cli\u003eM\u0026eacute;decins Sans Fronti\u0026egrave;res. 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Omadacycline for community-acquired bacterial pneumonia. \u003cem\u003eNew England Journal of Medicine, 380\u003c/em\u003e(6), 517\u0026ndash;527. https://doi.org/10.1056/NEJMoa1800201\u003c/li\u003e\n\u003cli\u003eTadros, M., Williams, V., Coleman, B. L., Johnstone, J., Borgia, S., \u0026amp; McGeer, A. (2013). Epidemiology and outcome of pneumonia caused by methicillin-resistant \u003cem\u003eStaphylococcus aureus\u003c/em\u003e (MRSA) in Canadian hospitals. \u003cem\u003ePLOS ONE, 8\u003c/em\u003e(9), e75171. https://doi.org/10.1371/journal.pone.0075171\u003c/li\u003e\n\u003cli\u003eTam, K., \u0026amp; Torres, V. J. (2019). \u003cem\u003eStaphylococcus aureus\u003c/em\u003e secreted toxins and extracellular enzymes. \u003cem\u003eMicrobiology Spectrum, 7\u003c/em\u003e(2). https://doi.org/10.1128/microbiolspec.GPP3-0039-2018\u003c/li\u003e\n\u003cli\u003eVentura, C. L., Higdon, R., Hohmann, L., Martin, D., Kolker, E., Liggitt, H. D., Skerrett, S. J., \u0026amp; Rubens, C. E. (2008). \u003cem\u003eStaphylococcus aureus\u003c/em\u003e elicits marked alterations in the airway proteome during early pneumonia. \u003cem\u003eInfection and Immunity, 76\u003c/em\u003e(12), 5862\u0026ndash;5872. https://doi.org/10.1128/IAI.00671-08\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Staphylococcus aureus, Lung inflammation, Virulence factors, Respiratory infection, Bacterial pneumonia","lastPublishedDoi":"10.21203/rs.3.rs-6857728/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6857728/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003e \u003cem\u003eStaphylococcus aureus\u003c/em\u003e is a commensal bacterium capable of transitioning into a pathogenic form under favorable conditions, resulting in a wide spectrum of infections. It accounts for approximately 20\u0026ndash;50% of hospital-acquired pneumonia (HAP) cases and 25.5% of community-acquired pneumonia (CAP), both of which are associated with substantial morbidity and mortality. The ability of \u003cem\u003eS. aureus\u003c/em\u003e to cause severe respiratory illness is of increasing clinical concern, particularly in settings with limited diagnostic and therapeutic resources.\u003c/p\u003e\u003ch2\u003eObjective\u003c/h2\u003e \u003cp\u003eThis study aimed to evaluate the histopathological alterations in lung tissues of Wistar rats experimentally infected with \u003cem\u003eS. aureus\u003c/em\u003e strains isolated from pneumonia patients, and to assess the severity of infection associated with different strains.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eA total of 1,500 sputum samples were collected from pneumonia patients in randomly selected hospitals across Nigeria. Standard microbiological techniques were employed for the isolation and identification of \u003cem\u003eS. aureus\u003c/em\u003e, yielding 79 positive isolates. These isolates were subcultured and used to inoculate healthy Wistar rats intranasally. After a 14-day incubation period, the rats were euthanized, and lung tissues were excised and processed for histological examination using hematoxylin and eosin (H\u0026amp;E) staining.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eHistopathological analysis revealed pronounced pulmonary lesions, including alveolar congestion, infiltration of inflammatory cells, thickening of alveolar septa, and accumulation of exudates and purulent material. Some strains\u0026mdash;CU82, CA26, CSA24, CU14, CA43, and CA58\u0026mdash;exhibited enhanced virulence, causing more severe tissue destruction.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eThis study demonstrates the substantial histopathological damage caused by \u003cem\u003eS. aureus\u003c/em\u003e-induced pneumonia and underscores the importance of strain-specific virulence in disease severity. The findings may inform clinical approaches to the diagnosis and management of \u003cem\u003eS. aureus\u003c/em\u003e-related pneumonia.\u003c/p\u003e","manuscriptTitle":"Histopathological Assessment of Lung Tissue in Wistar Rats with Pneumonia Induced by Staphylococcus aureus","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-23 07:15:29","doi":"10.21203/rs.3.rs-6857728/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"eef08f3b-94fb-4326-a1c2-0708c4731d2e","owner":[],"postedDate":"June 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-24T22:39:11+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-23 07:15:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6857728","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6857728","identity":"rs-6857728","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}