In the present study, a total of 512 food samples composed of raw milk, dairy products, meat/meat products, chicken meat, seafood and raw vegetables were analyzed for the presence of Listeria monocytogenes. The results of the standard identification methods showed that 20 (3.9%) of the analyzed samples were found to harbor this pathogen. Further, 8.4% (13/155) of chicken meats, 0.9% (1/105) of meat/meat products and 13.6% (6/44) of fresh vegetables were contaminated with L. monocytogenes. Interestingly, only 18 of these isolates gave expected band size when they were subjected to molecular confirmation by polymerase chain reaction (PCR). Multiplex PCR serotyping of the strains revealed that 66.6% (12/18) of which belonged to serotype 1/2a (or 3a), 5.6% (1/18) to serotype 1/2b (or 3b, 7), 5.6% (1/18) to serotype 1/2c (or 3c) and 11.1% (2/18) to serotype 4b (or 4d, 4e). Two strains could not be serotyped by multiplex PCR. The strains were also evaluated by disk diffusion assay for their susceptibility to 15 commonly used antimicrobials. Antimicrobial resistance was most frequently observed for clindamycin (94.4%), followed by streptomycin and kanamycin (88.9%); penicillin (72.2%), tetracycline and gentamicin (66.7%); quinopristin/dalfopristin and erythromycin (61.1). Interestingly, 13 strains were resistant to more than five antibiotics. All strains were susceptible to linezolid, teicoplanin and vancomycin.
Listeria monocytogenes is one of the most important foodborne pathogens responsible for several outbreaks and cases of listeriosis in human. This study focused on the prevalence of L. monocytogenes in different raw and ready-to-eat foodstuffs, and serotype distribution among the isolates. Antibiotic resistance profiles of the isolates were also reported. Information and relief provided to consumers could help elaborate public health and food safety.