Contamination sources, biofilm-forming ability and biocide resistance of Shiga toxin-producing Escherichia coli O157:H7 and non-O157 isolated from tilapia-processing facilities

Contamination sources, biofilm-forming ability and biocide resistance of Shiga toxin-producing Escherichia coli O157:H7 and non-O157 from two tilapia-processing plants were assessed. The application of unsuitable handling and sanitizing procedures caused a wide contamination by thermotolerant coliforms in Factories A (51.2% of points) and B (66.7%), exceeding the legal limits for frozen tilapia fillets. E. coli was also detected in both factories, but at low concentrations. RAPD-PCR using primers DAF4, GEN15001, and M13 characterized seven E. coli strains. Biofilm-forming ability of stx(2d)-carriers and E. coli O157:H7 strains (E3, E4, E5, E6, E7) was higher than nonvirulent strains (E2, E8). Biofilm formation was correlated with the type of origin surface (abiotic or biotic) and with the presence of fliC H7. Biofilms resisted doses of peracetic acid and sodium hypochlorite higher than those recommended by manufacturers. E. coli was more susceptible to peracetic acid than sodium hypochlorite, but their similar mechanisms of action could increase the risk of crossresistance. Practical applicationsCase-by-case approaches are recommended to determine the sources and degree of contamination present in food-processing facilities, which would allow applying precise responses that avoid, or at least reduce, the persistence of bacterial pathogens and the risk of antimicrobial resistance. Data obtained in this study showed that current strategies to control thermotolerant coliforms and E. coli in tilapia-processing facilities are ineffective and the application of sublethal doses have allowed the emergence of antimicrobial resistant strains. Therefore, novel working-safe, environmentally friendly and cost-effective biocides, and the development of innovative sanitizing procedures are required to control biofilms formed by bacterial pathogens in food-processing environments.