Characterization of Listeria monocytogenes in Palermo (Sicily, Italy) from 2018 to 2020: Correlation between Molecular and Clinical Data

Objectives: Listeria monocytogenes (LM), the etiological agent of Listeriosis, can cause foodborne zoonosis. In this study, we characterized 23 strains that caused human listeriosis in Palermo (Sicily, Italy) during the period 2018-2020. In addition, we assessed the phenotypic susceptibility of clinical isolates to antibiotics in accordance with EUCAST guidelines. Methods The serogroup was determined by PCR. While MLST and MVLST were identified through the sequencing of housekeeping genes. Finally, susceptibility to antibiotics was assessed by means of the Phoenix automatic system. Results Patients hospitalized with listeriosis were predominantly males (56% vs. 44% of females). The cases were not associated with pregnancy included patients >65 years of age (60%), two of whom were affected by cancer, while cases associated with pregnancy included two pregnant women and three preterm infants. Data collected found that the main pathologies shown by patients were meningitis (60,9%) and bacteremia (39,1%). The LM strains were isolated from blood (52%), cerebrospinal fluid (26%), cerebrospinal fluid + blood (13%), blood + nasal swab (4%), and ascitic fluid (4%). The predominant serogroup was IVb (96%), whereas only one strain belonged to serogroup IIa (4%). Among the strains with serotype 4b, 4d, 4e, ST 2/VT 21 (92%) and ST6/VT19 (4%) were determined, while only isolates with serotype 1/2a, 3a show ST155/VT45 (CC155). Conclusion This study revealed the widespread circulation of a single clinical strain (ST2/VT21) associated with suspected food contamination, demonstrating the importance of carrying out molecular epidemiological surveillance. Our clinical isolates were susceptible to the assayed beta-lactams, in agreement with the literature data.