The Polymorphic Aggregative Phenotype of Shiga Toxin-Producing Escherichia coli O111 Depends on RpoS and Curli

Abstract

T he global burden of Shiga toxin-producing Escherichia coli (STEC) infection is estimated to be 2.8 million cases of acute illnesses annually worldwide (1), and non-O157 STEC infections result in nearly 113,000 illnesses yearly in the United States (2). STEC O111 is among the six most commonly reported non-O157 STEC serogroups (3). It is the most prevalent STEC serogroup in Europe (4) and the third most important STEC serogroup in the United States, causing 19% of the illness cases in 2000 to 2010 (3). Outbreaks of STEC O111 illness also have been reported in Australia (5), Canada (6), and Japan (7). Many of the reported cases of STEC O111 infection in the United States are of sporadic illness. However, this serogroup has caused more than 15 well-known outbreaks in the United States since 1999 (8-10).We have previously assembled a collection of environmental and clinical strains of E. coli O111 from diverse sources and investigated various genotypic and phenotypic characteristics of these strains to gain a better understanding of the epidemiology and biology of this serogroup. Our study revealed that many environmental STEC O111 strains isolated from diverse sources over time and from various geographical locations are genotypically identical, suggesting that these strains circulate in the environment and may contaminate the food chain (11). The environmental and outbreak strains in this collection were similar in their virulence determinants, and all displayed a strong aggregative phenotype characterized by the settlement of large bacterial assemblages in broth culture with agitation; in contrast, the sporadic case strains, which are strains isolated from single patients that were not part of a recognized outbreak, were nonaggregative (11).Autoaggregation is caused by bacterial cell-cell interactions that lead to the production of a range of multicellular assemblages and, in some cases, may cause flocculation and settling of the cells in static liquid suspensions. A number of bacterial surface factors that are involved in E. coli interactions with host cells and virulence are also implicated in autoaggregation (12). These adhesins, which mediate the attachment of E. coli cells to one another and to human epithelial cells, include type I fimbriae, type IV bundleforming pili, AAF/I and AAF/II aggregative adherence fimbriae, and the autotransporter proteins TibA and Ag43 (12). In 2011, a strain of STEC O104:H4 that harbored the AAF virulence and aggregative adherence determinants of enteroaggregative E. coli (EAEC) caused a large outbreak in Germany (13), calling attention to bacterial aggregation as an important factor in epidemics of foodborne disease. The ability to form aggregates also may increase the tolerance of human pathogens to physicochemical stresses in host and in nonhost environments. Expression of the self-aggregative adhesins Ag43 and TibA in E. coli promotes the formation of single-and mixed-species biofilms (14, 15), and Ag43 and type IV bundle-forming pili enhance resistance to antimicrobial ag...

Conditional Function of Autoaggregative Protein Cah and Common cah Mutations in Shiga Toxin-Producing Escherichia coli

“…Like many other STEC strains, EDL933 and SS17 carry genes encoding adhesins known to play a role in biofilm formation and attachment to plant tissue, such as curli, cellulose, poly-N-acetylglucosamine, and colanic acid, as well as adhesins known to mediate adherence of E. coli O157:H7 to epithelial cells, such as long polar fimbriae, curli, pili, and other autotransporter proteins (11,13,18). In particular, curli fimbriae, which promote adhesion to abiotic and biotic surfaces such as human cells and plant surfaces (18), are known to trigger strong cell-cell interactions that result in autoaggregation (29), similarly to intercellular interactions via the self-recognizing adhesins Cah ( 14) and Ag43 (16). Some of these adhesins may interfere with Cah function or may strengthen the role of Cah in adhesion when they are expressed in a particular niche in E. coli.…”

“…Inactivation of RcsB or RpoS in E. coli O157:H7 was suggested to be beneficial to the bacterial population as a whole, since two subpopulations with an array of distinct phenotypes emerged. Remarkably, the polymorphic nature of autoaggregation observed in a collection of STEC O111 strains was attributed to loss-of-function mutations in RpoS (29,48), suggesting that adaptive mutation is a common mechanism in STEC to fine-tune its colonization and survival under changing habitat conditions.…”

Function, Evolution, and Composition of the RpoS Regulon in Escherichia coli

“…RpoS regulation of biofilm production is positive in E. coli K12 but is negative in O157:H7 strains (Carter et al, 2014). In both EHEC O157:H7 and STEC O111 (Diodati et al, 2016), RpoS contributes to autoaggregation through enhanced fimbriae production in strains attenuated in rpoS expression. Though the loss of RpoS can render the cell sensitive to stress, the benefit of increased pathogenesis probably outweighs the cost of loss of fitness.…”

EDL933 Strains of Escherichia coli O157 can Demonstrate Genetic Diversity and Differential Adherence to Bovine Recto-Anal Junction Squamous Epithelial Cells

“…As described previously, congo red binding and biofilm formation assays were set up to determine levels of curli fimbriae formation and are described briefly below [46]. E. coli strain K-12 MG1655, and O157 strains 86-24 WT and EDL933 WT ATCC 43895 that are established curli fimbriae producers were included as positive controls while E. coli O111 strain MB1068W that lacks the curli fimbriae was included as a negative control in these assays [46,54].…”