Biofilm-forming capacity of Escherichia coli isolated from cattle and beef packing plants: relation to virulence attributes, stage of processing, antimicrobial interventions, and heat tolerance

Abstract

AbstractDespite the importance of biofilm formation in contamination of meat by pathogenic Escherichia coli at slaughter plants, drivers for biofilm have been unclear. To identify selection pressures for biofilm, we evaluated 745 ‘Top 7’ from cattle and 700 generic E. coli from two beef slaughter plants for motility, expression of curli and cellulose, and biofilm-forming potential. Top 7 were also screened for serogroup, stx1, stx2, eae and rpoS. Generic E. coli were compared by source (hide of carcass, hide-off carcass, processing equipment) before and after implementation of antimicrobial hurdles. The proportion of E. coli capable of forming biofilms was lowest (7.1%; P < 0.05) for cattle isolates and highest (87.3%; P < 0.05) from equipment. Only one enterohemorrhagic E. coli (EHEC) was an extremely-strong biofilm-former, in contrast to 73.4% of E. coli from equipment. Isolates from equipment after sanitation had a greater biofilm-forming capacity (P < 0.001) than those before sanitation. Most Top 7 were motile and expressed curli, although these traits along with expression of cellulose and presence of rpoS were not necessary for biofilm formation. In contrast, isolates capable of forming biofilms on equipment were almost exclusively motile and able to express curli. Results of the present study indicate that cattle would rarely carry EHEC capable of making strong biofilms to slaughter plants. However, if biofilm-forming EHEC contaminated equipment, current antimicrobial hurdles would inadvertently perpetuate the most robust biofilm-forming strains. Accordingly, new and effective anti-biofilm hurdles are required for meat-processing equipment, to reduce future instances of food-borne disease.ImportanceAs the majority of enterohemorrhagic E. coli (EHEC) are not capable of forming biofilms, sources were undetermined of the biofilm-forming EHEC isolated from ‘high-event periods’ in beef slaughter plants. This study demonstrated that sanitation procedures used on beef-processing equipment inadvertently select for survival of the most robust biofilm-forming strains of E. coli. Cattle only rarely carry EHEC capable of forming strong biofilms (1/745 isolates evaluated), but sanitation of equipment markedly increased (P < 0.001) biofilm-forming capacity of E. coli. In contrast, chilling carcasses for 3 days at 0°C reduced (P < 0.05) biofilm-forming capacity of E. coli. Consequently, an additional anti-biofilm hurdle for meat-processing equipment, perhaps involving cold exposure, is necessary to further reduce the risk of food-borne disease.