Prevalence, genetic diversity and antimicrobial susceptibility of Listeria monocytogenes isolated from open-air food markets in Greece

A total of 210 food samples originating from milk products, ready-to-eat salads, raw meat and raw meat products purchased in ten open-air market places in Thessaloniki, Greece, were analyzed for the presence of Listeria monocytogenes. Thirty (14.3%) contained L. monocytogenes with the highest prevalence in raw meat (27.5%), raw meat products (18%) and cheese (8%). The strains were susceptible to 16 antimicrobials as determined by microbroth dilution, except one strain which displayed resistance to tetracycline (MIC > 32 μg/ml). This strain carried the tetracycline resistance gene tet(M). Pulsed-field gel electrophoresis (PFGE) revealed a low genetic diversity among the isolates, irrespective of their origin. This suggests that dominant L. monocytogenes clones are widespread in different food product types in open-air food markets in Greece. The high prevalence of L. monocytogenes in these products indicates that appropriate hygienic measures and periodic bacteriological controls are also necessary in open-air food markets to reduce contamination with food-borne pathogens. Greek specialties made with raw meat and raw milk may contain L. monocytogenes and should not be consumed by persons at risk.