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Applied and Environmental Microbiology, April 2006, p. 2564-2572, Vol. 72, No. 4
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.4.2564-2572.2006

Analyses of the Red-Dry-Rough Phenotype of an Escherichia coli O157:H7 Strain and Its Role in Biofilm Formation and Resistance to Antibacterial Agents

Gaylen A. Uhlich,^1* Peter H. Cooke,² and Ethan B. Solomon³

Microbial Food Safety Research Unit,¹ Microbial Biophysics and Residue Chemistry and Core Technologies Research Unit, Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, Pennsylvania,² DuPont Chemical Solutions Enterprise, Experimental Station Laboratory, P.O. Box 80402, Wilmington, Delaware³

Received 7 September 2005/ Accepted 2 February 2006

In a previous study, we identified Congo red-binding and -nonbinding phase variants of Escherichia coli serotype O157:H7 strain ATCC 43895. The Congo red-binding variant, strain 43895OR, produced a dry, aggregative colony that was similar to the red, dry, and rough (rdar) phenotype characteristic of certain strains of Salmonella. In contrast, variant 43895OW produced a smooth and white colony morphology. In this study, we show that, similar to rdar strains of Salmonella enterica serovar 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. enterica serovar 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 >4-fold-larger amounts of biofilm than strain 43895OW on polystyrene, glass, stainless steel, and Teflon; formation was >3-fold higher in rich medium than in nutrient-limited medium. Biofilm-associated 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.

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* Corresponding author. Mailing address: Eastern Regional Research Center, ARS, USDA, 600 East Mermaid Ln., Wyndmoor, PA 19038. Phone: (215) 233-6740. Fax: (215) 233-6581. E-mail: guhlich{at}errc.ars.usda.gov.

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Applied and Environmental Microbiology, April 2006, p. 2564-2572, Vol. 72, No. 4
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.4.2564-2572.2006

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