Biofilm formation by foodborne pathogens is a serious threat to food safety. Meat processing plants harbor various microorganisms, and the environmental microbial community might impact pathogen survival via mixed biofilm formation. This study investigated the effects of environmental microorganisms on *E. coli* O157:H7 sanitizer tolerance. Results showed that biofilm-forming ability and bacterial species composition varied based on plants and drain locations. *E. coli* O157:H7 cells had significantly higher sanitizer tolerance in mixed biofilms from the plant with recurrent *E. coli* O157:H7 prevalence. The mixed biofilm best protecting *E. coli* O157:H7 also had the highest species diversity. The unique environmental microbial community, biofilm formation, and interspecies interactions affect *E. coli* O157:H7 persistence.

Sapna Chitlapilly Dass, Joseph M. Bosilevac, Maggie Weinroth, Christian G. Elowsky, You Zhou, Angela Anandappa, Rong Wang