Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 7/1/2008
Publication Date: 8/25/2008
Citation: Uhlich, G.A. 2008. Investigation of E. coli O157:H7 Mixed-Species Biofilm Formation. Meeting Abstract. Interpretive Summary:
Technical Abstract: During 2006, there were three multi-state produce-associated outbreaks of E. coli O157:H7, two of which involved the state of Pennsylvania. In September, 26 states reported illnesses linked to spinach, which resulted in 205 confirmed cases of illness and 3 deaths (1). In November, 5 states reported illnesses that were linked to lettuce (2). Of 71 cases, 53 were hospitalized. Investigations have indicated that the produce involved in these outbreaks was most likely contaminated in the growing field with E. coli O157:H7 of animal origin. Bacterial persistence on foods or in the production environment can be augmented by biofilm formation. However, strains of E. coli serotype O157:H7 do not often form biofilms under laboratory growth conditions. In this study we compared the biofilm forming ability of 11 well-characterized O157:H7 food isolates to 7 Shiga toxin-producing E. coli strains from the spinach and lettuce outbreaks of 2006 that were submitted to the Pennsylvania Bureau of Labs. We also tested the ability of a non-biofilm-forming strain of O157:H7 from the spinach outbreak to persist on a solid surface when cultured together with a biofilm-forming E. coli serotype O-:H4 strain isolated from the same spinach bag. Results and Discussion The results of crystal violet biofilm assays performed on glass coupons indicate that strain O6E01767 (O-:H4) formed significantly greater amounts of biofilm on glass than the 17 E. coli O157:H7 strains in the study. None of the O157:H7 strains produced more biofilm than the un-inoculated control. These results confirm previous studies which have shown that E. coli O157:H7 is a poor biofilm-producing serotype. In mixed-species biofilm assays, we tested the ability of spinach isolate, O6F00475 (O157:H7), to persist on glass slides when cultured together with strain O6E01767 (O-:H4). Strains 06F00475 and 06E01767 were transformed with either plasmid pGFPuv or pUC19 and were differentiated in mixed samples by colony fluorescence on agar. While strain 06F00475 containing either plasmid could not be consistently recovered from biofilms formed on glass, strain 06E01767 was recovered in 4 log10 CFU/ml in single species or mixed strain biofilms. When cultured together, the recovered numbers of strain 06E01767, carrying either plasmid, were lower (P<0.05) than the numbers of total cells or strain 06F00475 indicating that the non-biofilm-forming strain, 06F00475 persisted in numbers greater than the biofilm-forming strain, 06E01767. This study clearly demonstrates that in situations where environmental contamination with enteric bacteria results in the mixed species contamination of food products, non-virulent biofilm-forming isolates could play an important role in the persistence of serotype O157:H7 on solid surfaces. References 1. http://www.dhs.ca.gov/ps/fdb/local/PDF/2006%20Spinach%20Report%20Final%20redacted.PDF. 2. http://www.cdc.gov/ecoli/2006/december/121406.htm.