Distribution Characterization Of Listeria Monocytogenes In Foods In Shanghai And Analysis Of Its Biofilm Formation Ability

Listeria monocytogenes is a common foodborne pathogen, which generally causes human illness including meningitis, meningoencephalitis and abortion with a high fatality rate of 20-30%. It is widely distributed in the environment and forms biofilms on food processing equipments. The resistance of L. monocytogenes in biofilm to disinfectant is significantly increased, thus the pathogen can contaminate food repeatedly and threaten public hygiene and human health.A total of 648 food samples were collected in Shanghai over a period from June 2013 to June 2014. The overall prevalence percentage of L. monocytogenes was 6.17%(n = 40). The detection rate was 15.96%(15/94) for raw meat, 4.16%(7/168) for raw milk, 9.90%(10/101) for quick-frozen food, 2.02%(2/99) for vegetables, 7.27%(4/55) for cooked meat and 4.17%(2/48) for aquatic product, respectivly, while it was negative for milk products(0/53) and bean products(0/30). The presence of L. monocytogenes in raw meat and quick-frozen food were higher than others, suggesting that these products constitute the main problem.Serotyping and ERIC-PCR were used for subtyping analyses of all the L. monocytogenes(n=86) isolated from the 40 positive food samples. All the L. monocytogenes isolates were divided into four serotypes by mutiplex PCR and agglutination test as follows : 1/2a(n=62), 1/2b(n=17), 1/2c(n=4) and 3c(n=3). Epidemiologically important serotype 1/2a and 1/2b were predominant(91.9%) in the 86 isolates. At the relative similarity coefficient of 0.80, 86 isolates and 4 reference strains were classfied into 10 clusters and 8 singletons by ERIC-PCR. It was found that the L. monocytogenes isolates shared the same serogroup could be clustered together by ERICPCR at a certain relative similarity coefficient, while isolates belonging to the same serogroup could be efficiently distinguished according to diverse ERIC-PCR profiles. Furthermore, our results will provide the fundamental data for epidemiological surveillance of L. monocytogenes.Biofilm-forming ability of forty L. monocytogenes strains previously isolated from positive food sample was assessed by crystal violet staining. Most strains showed different biofilm-forming abilities and the OD595 value range from 0.37 to 1.62. Polytropic biofilm formation was observed in serotype 1/2b strains. In addition, strains with a high biofilm-forming ability were more likely found in frozen food. The efficacy of the industrial disinfectants chlorine dioxide(Cl O2) and hydrogen peroxide(H2O2) against biofilms was also examined in terms of minimum biofilm eradication concentration(MBEC). Biofilms showed different antimicrobial resistance. H2O2 resistance increased as biofilms increased, but no correlation was found between the efficacy of Cl O2 and biofilms biomass. Cl O2 was found to be more effective against biofilms, while H2O2 could not be able to kill all the cells in biofilms at the recommended concentrations from national standard.