Mixed Biofilm Formation by Shiga Toxin–Producing Escherichia coli and Salmonella enterica Serovar Typhimurium Enhanced Bacterial Resistance to Sanitization due to Extracellular Polymeric Substances

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.

Comparison of the Antimicrobial and Sanitizer Resistance of Salmonella Isolates from Chicken Slaughter Processes in Korea

“…In this study, the majority of the 82 isolates exhibited recovery growth at various levels after sanitization treatment (Table and ). This is in agreement with previous reports showing that, although treatment with commonly used sanitizers at recommended concentrations can significantly reduce the number of viable biofilm cells, those treatments are unable to eliminate viable bacteria completely (Wang and others ; Wang and others ). In addition, the effectiveness of sanitization is highly strain‐dependent (Wang and others ; Wang and others ).…”

“…This is in agreement with previous reports showing that, although treatment with commonly used sanitizers at recommended concentrations can significantly reduce the number of viable biofilm cells, those treatments are unable to eliminate viable bacteria completely (Wang and others ; Wang and others ). In addition, the effectiveness of sanitization is highly strain‐dependent (Wang and others ; Wang and others ). In a study of Corcoran and others (), the effects of sodium hydroxide, sodium hypochlorite, and benzalkonium chloride on Salmonella biofilms have been determined.…”

“…They exhibited high resistance to sanitization as well as recovery capability (data not shown). This is in agreement with previous reports showing that biofilm‐forming bacteria are generally more resistant to physical and chemical treatments due to the 3‐dimensional structure of the biofilm and multiple layers of bacterial cells with copious extracellular material (Wang and others ; Wang and others ). In this study, the majority of the 82 isolates exhibited recovery growth at various levels after sanitization treatment (Table and ).…”

Identification of ypqP as a New Bacillus subtilis Biofilm Determinant That Mediates the Protection of Staphylococcus aureus against Antimicrobial Agents in Mixed-Species Communities

“…YpqP is likely involved in the production of "public goods" that can protect biofilm inhabitants against the actions of biocides (70,71). These findings underline the importance of studying the interactions between pathogens and resident microflora, such as the ubiquitous bacterium B. subtilis, to develop efficient control strategies against infectious microorganisms.…”

The Behavior of Staphylococcus aureus Dual-Species Biofilms Treated with Bacteriophage phiIPLA-RODI Depends on the Accompanying Microorganism

“…Indeed, multispecies interactions in mixed biofilms are known to affect resistance to disinfectants (3). For instance, the presence of a curli-producing Escherichia coli strain was found to protect Salmonella enterica serovar Typhimurium biofilm cells from chlorine (4). Additionally, the matrix of mixed-species biofilms often presents greater biochemical complexity compared with that of the matrix of singlespecies communities (5).…”