Protective role of Acinetobacter and Bacillus for Escherichia coli O157:H7 in biofilms against sodium hypochlorite and extracellular matrix-degrading enzymes

Foodborne pathogenic bacteria in multi-species biofilms in food manufacturing facilities have been suspected to be the cause of cross-contamination leading to foodborne illness. We studied if cafeteria kitchen-associated bacterial isolates can have any protective effect on E. coli O157:H7 in biofilm against extracellular polymeric substances (EPS)-degrading enzymes and sodium hypochlorite. We investigated multi-species biofilm-forming ability and the efficacy of EPS-degrading enzymes using crystal violet assay. The susceptibility of E. coli O157:H7 to sodium hypochlorite (NaClO) was evaluated using propidium monoazide combined with quantitative PCR (PMA-qPCR). Then, a combined treatment with enzymes followed by NaClO was also tested. Most cafeteria kitchen isolates of Acinetobacter and Bacillus were able to form biofilms. Several of them showed a protective effect on E. coli O157:H7 against NaClO after forming multi-species biofilms, particularly in Acinetobacter. This protective effect on E. coli O157:H7 was also noticed after the enzyme or the combined treatment with NaClO. Our results give us an insight into the protective role of food-associated environmental bacteria for E. coli O157:H7 in biofilms against common sanitizers and warrant further study to develop effective control methods. Our study also highlights the importance of preventing contamination or biofilm formation by environmental microorganisms, eventually reducing foodborne illness.