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
Stanford, K., Tran, F., Zhang, P., Yang, X. (2021). 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. Applied and Environmental Microbiology, [online] 87(23), http://dx.doi.org/10.1128/AEM.01126-21
Plain language summary
Biofilms are a challenging problem for the food industry. Better understanding of conditions that would select for biofilm formers would be of value to the ultimate control of biofilm formers. In this work, we have assessed the biofilm forming ability of a large population of E. coli from cattle (n=754) of various serotypes, and of E. coli (n=700) from various stages of beef processing. We found that most E. coli from animals were poor biofilm formers. However, E. coli from equipment, in particular after cleaning had the highest proportions of biofilm formers, suggesting biofilm forming ability may have resulted their greater survival. On the other hand, the air chilling process implemented at one plant greatly reduced the proportion of biofilm forming E. coli, and this could be further explored as biofilm control strategies.
Despite the importance of biofilm formation in the contamination of meat by pathogenic Escherichia coli at slaughter plants, drivers for biofilm remain unclear. To identify selection pressures for biofilm, we evaluated 745 isolates from cattle and 700 generic E. coli isolates from two beef slaughter plants for motility, the expression of curli and cellulose, and biofilm-forming potential. Cattle isolates were also screened for serogroup, stx1, stx2, eae, and rpoS. Generic E. coli isolates were compared by source (hide of carcass, hide-off carcass, and processing equipment) before and after the implementation of antimicrobial hurdles. The proportion of E. coli isolates 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) isolate was an extremely strong biofilm former, in contrast to 73.4% of E. coli isolates from equipment. Isolates from equipment after sanitation had a greater biofilm-forming capacity (P, 0.001) than those before sanitation. Most cattle isolates were motile and expressed curli, although these traits along with the expression of cellulose and the detection 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. The results of the present study indicate that cattle rarely carry EHEC capable of making strong biofilms in slaughter plants. However, if biofilm-forming EHEC contaminates equipment, current sanitation procedures may not eliminate the most robust biofilm-forming strains. Accordingly, new and effective antibiofilm hurdles for meat-processing equipment are required to reduce future instances of foodborne disease. IMPORTANCE As the majority of enterohemorrhagic E. coli (EHEC) isolates are not capable of forming biofilms, sources were undetermined for biofilm-forming EHEC isolated from “high-event periods” in beef slaughter plants. This study demonstrated that sanitation procedures used on beef-processing equipment may inadvertently lead to the survival of robust biofilm-forming strains of E. coli. Cattle only rarely carry EHEC capable of forming strong biofilms (1/745 isolates evaluated), but isolates with greater biofilm-forming capacity were more likely (P, 0.001) to survive equipment sanitation. In contrast, chilling carcasses for 3 days at 0°C reduced (P, 0.05) the proportion of biofilm-forming E. coli. Consequently, an additional antibiofilm hurdle for meat-processing equipment, perhaps involving cold exposure, is necessary to further reduce the risk of foodborne disease.