Inactivation of Escherichia coli O157:H7 on stainless steel upon exposure to Paenibacillus polymyxa biofilms

We investigated the potential use of biofilm formed by a competitive-exclusion (CE) microorganism to inactivate Escherichia coli O157:H7 on a stainless steel surface. Five microorganisms showing inhibitory activities against E. coli O157:H7 were isolated from vegetable seeds and sprouts. The microorganism with the greatest antimicrobial activity was identified as Paenibacillus polymyxa (strain T5). In tryptic soy broth (TSB), strain T5 reached a higher population at 25°C than at 12 or 37°C without losing inhibitory activity against E. coli O157:H7. When P. polymyxa (6logCFU/mL) was co-cultured with E. coli O157:H7 (2, 3, 4, or 5logCFU/mL) in TSB at 25°C, the number of E. coli O157:H7 decreased significantly within 24h. P. polymyxa formed a biofilm on stainless steel coupons (SSCs) in TSB at 25°C within 24h, and cells in biofilms, compared to attached cells without biofilm formation, showed significantly increased resistance to a dry environment (43% relative humidity [RH]). With the exception of an inoculum of 4logCFU/coupon at 100% RH, upon exposure to biofilm formed by P. polymyxa on SSCs, populations of E. coli O157:H7 (2, 4, or 6logCFU/coupon) were significantly reduced within 48h. Most notably, when E. coli O157:H7 at 2logCFU/coupon was applied to SSCs on which P. polymyxa biofilm had formed, it was inactivated within 1h, regardless of RH. These results will be useful when developing strategies using biofilms produced by competitive exclusion microorganisms to inactivate foodborne pathogens in food processing environments.