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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Produce Safety and Microbiology Research » Research » Publications at this Location » Publication #252797
Title: Phenotypic Divergence in Curli Variants of Enterohemorrhagic Escherichia coli O157:H7

Author
item Carter, Michelle
item Brandl, Maria
item Kyle, Jennifer
item Louie, Jacqueline
item Huynh, Steven
item Parker, Craig
item Carychao, Diana
item Cooley, Michael
item Bates, Anne
item Mandrell, Robert

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/4/2010
Publication Date: N/A
Citation: N/A

Interpretive Summary: Bacteria found in natural environments are often associated with other microbial species and are present in a structured community referred as biofilm. Growth as a biofilm confers great survival advantages for bacteria including human pathogens as it provides protection from various environmental stresses. Curli is a bacterial appendage found in many enteric bacteria and it enhances the initial attachment of bacteria to solid surface and subsequently, the formation of biofilm. Variations in curli production were reported in enterohemorrhagic E. coli O157:H7 (EcO157), which is the most common enterohemorrhagic E. coli serotype and contributes significantly to human infections and outbreaks in the US, and is a major public health concern. In this study, we aimed at understanding the ecological significance of maintaining curli variants in the EcO157 population. We first assembled an array of clinical and environmental isolates that were highly related to several US outbreak strains including strains linked to the 2006 spinach outbreak. We then isolated the curli variants by growing them on a curli indicating plate (congo red plate): red colonies that formed on the congo red plate were curli-producing (C+) variants whereas white colonies that formed on the congo red plate were curli-deficient (C-) variants. We then compared the curli variants of each strain for their anaerobic growth, metabolic fingerprints, and survival in acidified medium (pH 2.5), a condition that mimics the human gastric pH. Higher growth rates were observed for C- variants at 37°C under anaerobiosis whereas their ability to use an array of sugars and amino acids under aerobic conditions was significantly reduced. C+ variants were much more sensitive to acidic pH than C- variants. The higher growth rates under anaerobiosis and survival under acidic pH of the C- variants suggest that maintaining curli variants in EcO157 populations may promote rapid adaptation to the human host environment.

Technical Abstract: Curli are adhesive fimbriae of many Enterobactericeae and are involved in surface attachment, cell aggregation, and biofilm formation. They also mediate host cell invasion and are potent inducers of the host inflammatory response. Variations in curli expression were reported in enterohemorrhagic E. coli O157:H7 (EcO157). Our study aimed at understanding the ecological significance of maintaining curli variants in the EcO157 population. We first assembled an array of clinical and environmental isolates that were highly related to several US outbreak strains including strains linked to the 2006 spinach outbreak. The curli variants were isolated by growing bacteria on congo red plates: red colonies were curli-producing (C+) variants whereas white colonies were curli-deficient (C-) variants. The clonal relationship between curli variants of each strain was verified by MLVA typing. All C+ variants were able to produce curli at 37°C. We then compared the curli variants of each strain for their anaerobic growth, metabolic fingerprints, and survival in acidified medium (pH 2.5), a condition that mimics the human gastric pH. Higher growth rates were observed for C- variants at 37°C under anaerobiosis whereas their ability to use an array of sugars and amino acids under aerobic conditions was significantly reduced. C+ variants were much more sensitive to acidic pH than C- variants. After acid challenge at 37°C for 2 h, the average percentage of survival for C+ variants were 2.0-, 5.0-, and 5.2-log fold less than their corresponding C- variants for strains related to outbreaks linked to spinach (2006), hamburger (1993), and lettuce (2006), respectively. When the acid challenge was increased to 6 h, the difference in acid tolerance (% of survival) between curli variants related to the 2006 spinach outbreak strains increased to 4.7- and 6.0-log fold for clinical and environmental isolates, respectively. The higher growth rates under anaerobiosis and survival under acidic pH of the C- variants suggest that maintaining curli variants in EcO157 populations may promote rapid adaptation to the human host environment.