Ethanolamine-regulated fimbriae in enterohemorrhagic Escherichia coli O157:H7 pathogenesis

Ethanolamine (EA) is a signal for recognition of the host environment and regulation of virulence gene expression in enterohemorrhagic Escherichia coli O157:H7 (EHEC). Preliminary data suggested that EA increased early EHEC attachment to epithelial cells and also promoted a clustering adherence phenotype with other bacterial cells, which is classically mediated by fimbriae in bacteria. EHEC encodes sixteen fimbrial loci, and most were thought to be cryptic or incomplete. We hypothesize that EA promotes the expression of EHEC fimbriae and that these fimbriae are critical for EHEC colonization of the gastrointestinal (GI) tract. Expression of genes encoded in fifteen EHEC fimbrial loci was increased during growth with EA in comparison to growth without EA, and this increase in fimbrial transcription correlated with an increase in fimbrial structures present on the bacterial surface. We further characterized the expression of four EA-regulated fimbrial loci and found that all necessary subunits for fimbrial assembly are transcribed, suggesting that these four loci encode functional fimbriae. Together, these data demonstrate transcription of EHEC fimbriae, several for the first time, and suggest that they may be functional. To begin to elucidate the roles of EHEC fimbriae in colonization, we constructed deletion strains in two EA-regulated fimbriae, Erf1 and Erf2. Neither Erf1 nor Erf2 were necessary for early attachment to epithelial cells in vitro; however, these two EA-regulated fimbriae directed the expression of EHEC virulence determinants important for later stages in infection, including Shiga toxin and the locus of enterocyte effacement (LEE). Additionally, Erf1 contributed significantly to EHEC colonization in a murine model of infection. Our findings demonstrate expression of EHEC fimbriae in response to the biologically relevant molecule EA, elucidate the contribution of fimbriae to EHEC early attachment to epithelial cells, and define a pivotal role for fimbriae in pathogenesis, beyond mediating attachment, as regulators of virulence gene expression.