Title: Growth media and temperature effects on biofilm formation by serotype O157:H7 and non-O157 Shiga toxin-producing Escherichia coli Authors
Submitted to: FEMS Microbiology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 2014
Publication Date: May 20, 2014
Citation: Uhlich, G.A., Chen, C., Cottrell, B.J., Nguyen, L.T. 2014. Growth media and temperature effects on biofilm formation by serotype O157:H7 and non-O157 Shiga toxin-producing Escherichia coli. FEMS Microbiology Letters. DOI: 10.1111/1574-6968.12439. Interpretive Summary: Shiga toxin-producing strains of Escherichia coli (STEC) are important causes of foodborne illness. Under stressful conditions, such as low temperatures or during nutrient shortages, certain bacteria growing on surfaces can attach together using protein fibers and encase themselves in a protective polysaccharide matrix (biofilm formation). The most common protein fiber and polysaccharide used by E. coli are curli fibers and cellulose. Both curli and cellulose, when expressed by E. coli growing on agar plates containing the dye Congo red, will take up the dye causing the bacterial colony to turn red. This provides an easy method for identifying strains capable of expressing curli and cellulose. However, growth media composition and incubation temperature can affect dye affinity and impose limitations on our ability to identify strains by this method. In this study we test two different media at three different temperatures and identify the ideal conditions for utilization of the Congo red dye procedure. The results of this study will allow us to more accurately detect biofilm-forming foodborne pathogens and develop strategies for their inactivation.
Technical Abstract: Biofilm formation in most Escherichia coli strains is dependent on curli fimbriae and cellulose, and the expression of both varies widely among pathogenic strains. Curli and cellulose expression are often identified by their affinity for Congo red dye (CR). However, media composition and incubation temperature can affect dye affinity and impose limitations on phenotype detection by this method. In this study we compared different Shiga toxin-producing E. coli for CR affinity and biofilm formation under different media/temperature conditions. We found strain and serotype differences in CR affinities and biofilm production, as well as temperature and media requirements for maximum affinity. We also constructed strains with deletions of curli and/or cellulose genes to determine their contributions to the phenotypes and identified two O45 strains with a media-dependent induction of cellulose.