ANALYSIS OF THE "RDAR" PHENOTYPE OF A STRAIN OF ESCHERICHIA COLI O157:H7 AND ITS ROLE IN BIOFILM FORMATION AND RESISTANCE TO ANTIBACTERIAL AGENTS

Authors: Uhlich, Gaylen; Cooke, Peter; SOLOMON, ETHAN - DUPONT CHEM. SOLUTIONS EN

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2006
Publication Date: 2/1/2006
Citation: Uhlich, G.A., Cooke, P.H., Solomon, E.B. 2006. Analysis of the "rdar" phenotype of a strain of escherichia coli o157:h7 and its role in biofilm formation and resistance to antibacterial agents. Applied and Environmental Microbiology. Vol. 72:2564-2572.

Interpretive Summary: In a previous study we identified a genetic mutant of E. coli O157:H7 that was able to switch back and forth between cells that expresses surface fimbriae designated as "curli fibers" (strain 43895OR) and a strain that does not (strain 43895OW). The appearence of the colonies of the curli-producing strain, strain 43895OW, is similar to colonies of curli-producing strains of Salmonella which are capable of forming dense biofilms. In this study we show that the curliated strain, 43895OR, has many of the same properties as the Salmonella strains. However, strain 43895OR does not produce the polysaccharide, cellulose, which is important in the formation of Salmonella biofilms. When we tested strain 43895OR for biofilm formation, we found that it formed biofilms on glass, stainless steel, Teflon, and plastic, and was unable to do so in several different types of media. We also showed that the cells within the biofilm had a greater capacity to resist the killing affects of microbiocidal agents such as hydrogen peroxide and quaternary ammonium sanitizers on surfaces. This study shows that the curli-producing strain, 43895OR, can produce protective biofilms on a variety of surfaces commonly found in food processing plants. However, this strain of E. coli O157:H7 has some additional components involved in biofilm formation which are different than those of biofilm-producing strains of Salmonella. This strain will be used to investigate the components of E. coli biofilms and how they are regulated. This data will be useful for developing strategies to inhibit biofilm development.

Technical Abstract: In a previous study we identified Congo red-binding and -nonbinding phase variants of Escherichia coli serotype O157:H7 strain 43895. The Congo red-binding variant, strain 43895OR, produced a dry, aggregative colony that was simular to the red, dry and rough (rdar) phenotype characteristic of certain strains of Salmonella. In contrast, variant 43895OW produced a smooth and white (saw) colony morphology. In this study we show that, like the rdar strains of S. Typhimurium, strain 43895OR forms large aggregates in broth cultures, firm pellicles at the air-medium interface on glass, and dense biofilms on glass and polystyrene. However, unlike S. Typhimurium, strain 43895OR does not stain positive for cellulose production. When strain 43895OR was fixed on agar, scanning electron microscopy showed cells expressing extracellular matrix (ECM) containing curli fibers. Strain 43895OW was devoid of any ECM or curli fibers on agar, but showed expression of curli fibers during attachment to glass. Strain 43895OR produced more than 4-fold greater amounts of biofilm than strain 43895OW on polystyrene, glass, stainless steel, and Teflon, and formation was more than 3-fold greater in rich media than in nutrient-limited media. Biofilm cells of both strains showed statistically greater resistance (p<0.05) to hydrogen peroxide and quaternary ammonium sanitizer than their respective planktonic cells. This study shows that the rdar phenotype of E. coli O157:H7 strain 43895OR is important in multicellular growth, biofilm formation, and resistance to sanitizers. However, the lack of cellulose production by strain 43895OR indicates important differences in the ECM composition compared to that of Salmonella.