Antimicrobial Susceptibility of Porphyromonas Gingivalis Strains Isolated From Periodontal Patients by Three Testing Protocols

Abstract Background: The main goal of antimicrobials is to eliminate microorganisms that persists despite mechanical treatment. This is the case of Porphyromonas gingivalis (Pg), frequently isolated in patients with periodontitis. Global antibiotic studies evaluated in randomized clinical trials and in vitro studies have shown mixed results regarding effectiveness and susceptibility, even with different protocols where it is not clear if the laboratory test applied can affect the results. This information is relevant in order to obtain clinical outcomes and prevent antimicrobial resistance for their over-prescription or inadequate choice. The objective of this study was to describe the antimicrobial susceptibility in vitro of Pg to metronidazole, clindamycin, amoxicillin plus clavulanate, moxifloxacin and azithromycin in periodontal patients by three testing protocols.Methods: Microbiological samples were obtained in patients with a diagnosis of generalized moderate or severe periodontitis. They were incubated in anaerobic conditions for up to 7 days, and those morphologically compatible with Pg were isolated and identified by a mass spectrometer (MALDI-TOF MS). The three most frequently protocols for antimicrobials susceptibility tests (Blood agar- McFarland 0.5- Epsilometer test; Brucella blood agar- McFarland 1.0- Epsilometer test; Brucella blood agar- McFarland 0.5-Agar dilution) were applied to the same strain describing their profile and reporting any difference between the tests. The breakpoints considered the guidelines of CLSI and previous publications.Results: 50 patients (25 women, 25 men) with periodontitis between 34-69 years were selected. Finally, 25 Pg positives strains (50%) were recovered for the susceptibility analysis and all of them were highly sensitive to all antibiotics (range 96%-100%). Only one strain was resistant to azithromycin in one protocol, and no differences were found in the susceptibility results between the three tests.Conclusion: The Pg strains were highly susceptible to the five antibiotics evaluated in this population, showed a high level of susceptibility and significant agreement between the three tests applied, therefore the type of laboratory test used had not impacted on clinical interpretation. These findings are positives in terms of susceptibility and would provide several antibiotics treatment alternatives, and its prescription could be the best choice for the patient's specific context.