Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2013
Publication Date: 9/10/2013
Publication URL: http://handle.nal.usda.gov/10113/57718
Citation: Wang, R., Kalchayanand, N., Schmidt, J.W., Harhay, D.M. 2013. Mixed biofilm formation by Shiga toxin-producing Escherichia coli and Salmonella enterica serovar typhimurium enhanced bacterial resistance to sanitization due to extracellular polymeric substances. Journal of Food Protection. 76(9):1513-1522.
Interpretive Summary: Shiga-toxin producing Escherichia coli (STEC) O157:H7 and Salmonella Typhimurium are important foodborne pathogens capable of causing severe illness in humans. Bacteria form biofilms as a method of surviving stresses that may be placed on them. Biofilms are layers of bacteria that provide protection by shielding the inner layers from potential harm. Biofilms can be formed from a single species or in multispecies biofilm communities. Bacteria in biofilms are more resistant to sanitization than their counterparts in suspensions, and when detached, may lead to food contamination. We investigated how coexistence of STEC O157:H7 and Salmonella Typhimurium strains would affect bacterial growth competition and mixed-biofilm composition, as well as how mixed biofilm formation would affect bacterial resistance to common sanitizers. We found that Salmonella Typhimurium strains were able to outcompete STEC strains in suspension growth, however, mixed biofilm development was highly dependent upon companion strain properties in terms of the presence of certain bacterial cell surface structures. These observations indicate that certain cell surface structures not only enhance sanitizer resistance but also render protection to their companion strains regardless of species in mixed biofilms. Since bacterial coexistence is frequently seen in the environment, our study highlights the potential risk of cross-contamination by multispecies biofilms in food safety and calls for increased attention to proper sanitization practice in food processing facilities.
Technical Abstract: Shiga toxin–producing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium are important foodborne pathogens capable of forming single-species biofilms or coexisting in multispecies biofilm communities. Bacterial biofilm cells are usually more resistant to sanitization than their planktonic counterparts, so these foodborne pathogens in biofilms pose a serious food safety concern. We investigated how the coexistence of E. coli O157:H7 and Salmonella Typhimurium strains would affect bacterial planktonic growth competition and mixed biofilm composition. Furthermore, we also investigated how mixed biofilm formation would affect bacterial resistance to common sanitizers. Salmonella Typhimurium strains were able to outcompete E. coli strains in the planktonic growth phase; however, mixed biofilm development was highly dependent upon companion strain properties in terms of the expression of bacterial extracellular polymeric substances (EPS), including curli fimbriae and exopolysaccharide cellulose. The EPS-producing strains with higher biofilm-forming abilities were able to establish themselves in mixed biofilms more efficiently. In comparison to single-strain biofilms, Salmonella or E. coli strains with negative EPS expression obtained significantly enhanced resistance to sanitization by forming mixed biofilms with an EPS-producing companion strain of the other species. These observations indicate that the bacterial EPS components not only enhance the sanitizer resistance of the EPS- producing strains but also render protections to their companion strains, regardless of species, in mixed biofilms. Our study highlights the potential risk of cross-contamination by multispecies biofilms in food safety and the need for increased attention to proper sanitization practices in food processing facilities.