Prevalence, antibiotic resistance and genetic diversity of Listeria monocytogenes isolated from retail ready-to-eat foods in China

- High prevalence of Listeria monocytogenes was primarily determined in RTE foods in China.
- L. monocytogenes isolates was showed high antibiotic resistance.
- All serovars were found in positive isolates except serovar 4a/4c.
- ERIC-PCR and REP-PCR subtyping were used for genetic diversity analyses.

Listeria monocytogenes is a major foodborne pathogen that is well known as high mortality rate upon infected. This study aimed to investigate the prevalence of L. monocytogenes isolates from retail ready-to-eat (RTE) foods in China and characterize the isolates of L. monocytogenes by antibiotic resistance, serotyping, ERIC-PCR and REP-PCR subtyping analyses. From September 2012 to January 2014, a total of 364 retail RTE foods were obtained. Using the qualitative and quantitative methods, 25 samples (6.87%) were positive for L. monocytogenes. The identity of isolates of L. monocytogenes was confirmed by PCR. All 80 isolates in this survey were sensitive to penicillin and mezlocillin, the highest resistance is clindamycin (51.25%), followed by cephalothin (23.75%) and ampicillin (12.5%). Twenty-seven isolates were susceptible to all 14 tested antibiotics; seventeen isolates were resistant to more than two antibiotics, including six multiresistent strains resist to more than 10 antibiotics. L. monocytogenes isolates belonged to serovar types 1/2a (3a), 4b (4d, 4e), 1/2b (3b, 7) and 1/2c (3c). 29 L. monocytogenes isolates were selected by serotyping. At the relative similarity coefficient of 0.80, it grouped 29 isolates and 5 reference strains into 2 clusters and 3 singletons, 4 clusters and 1 singleton by ERIC-PCR and REP-PCR, respectively. Our study reflects the potential risk of L. monocytogenes infection in China. We also provide a comprehensive surveillance on its incidence on the RTE foods of L. monocytogenes and ensure more accurate treatment of human listeriosis with effective antibiotics.