Molecular characterization of Listeria Monocytogenes -

Abstract

Background: Listeria monocytogenes is an opportunistic intracellular pathogen that can survive harsh conditions, invade and spread into host cells. It is widespread in nature and has acquired resistance to many commonly used antimicrobials. This bacterium is the agent of listeriosis, a foodborne disease which is life threatening for immunocompromised patients and pregnant women. It harbors a number of genes encoding for virulence factors important in its pathogenesis and has the potential of producing biofilms rendering the organism resistant to antimicrobial agents. L.monocytogenes is not routinely screened for in Lebanon and there is lack of data about the prevalent strains and their potential pathogenicity. To that purpose, this study was undertaken in order to characterize L. monocytogenes from various food products, by evaluating resistance to commonly used antimicrobial agents, assessing the in vitro biofilm forming ability, detecting their virulence potential, and characterizing them at the strain level. Methods: Fifty-nine isolates were obtained from the Lebanese Agriculture Research Institute (LARI). These isolates were collected in 2012-2013 from local and imported food products in the Lebanese market. L. monocytogenes strains from the Centers for Disease Control and Prevention (CDC) were used as controls. Antimicrobial susceptibility testing was done by the disc diffusion technique and biofilm formation was measured using the Microtiter Plate Assay. Polymerase Chain Reaction (PCR) analysis was performed to detect the presence of the three main virulence genes; hly, actA, and inlB. Pulsed Field Gel Electrophoresis (PFGE) and BIONUMERICS analysis was carried out on all isolates to determine genomic relatedness. Results: Antimicrobial Susceptibility testing (AST) demonstrated resistance to oxacillin (n= 59; 100percent), ampicillin (n= 15; 25.43percent), penicillin (n= 30; 50.85percent), and clindamycin (n= 39; 66.1percent). Lebanese isolates from cheese and raw meat showed higher biofilm formation than imported and Lebanese se