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The human pathogen enterohemorrhagic Escherichia coli (EHEC) O157:H7 colonizes the rectoanal junction (RAJ) in cattle, its natural reservoir. Colonization at the RAJ poses a serious risk for fecal shedding and contamination of the environment. We previously demonstrated that EHEC senses acyl-homoserine lactones (AHLs) produced by the microbiota in the rumen to activate the gad acid resistance genes necessary for survival through the acidic stomachs in cattle and to repress the locus of enterocyte effacement (LEE) genes important for colonization of the RAJ, but unnecessary in the rumen. Devoid of AHLs, the RAJ is the prominent site of colonization of EHEC in cattle. To determine if the presence of AHLs in the RAJ could repress colonization at this site, we engineered EHEC to express the Yersinia enterocolitica AHL synthase gene yenI, which constitutively produces AHLs, to mimic a constant exposure of AHLs in the environment. The yenI(+) EHEC produces oxo-C6-homoserine lactone (oxo-C6-HSL) and had a significant reduction in LEE expression, effector protein secretion, and attaching and effacing (A/E) lesion formation in vitro compared to the wild type (WT). The yenI(+) EHEC also activated expression of the gad genes. To assess whether AHL production, which decreases LEE expression, would decrease RAJ colonization by EHEC, cattle were challenged at the RAJ with WT or yenI(+) EHEC. Although the yenI(+) EHEC colonized the RAJ with efficiency equal to that of the WT, there was a trend for the cattle to shed the WT strain longer than the yenI(+) EHEC.

infection and immunity

The Acyl-Homoserine Lactone Synthase YenI from Yersinia enterocolitica Modulates Virulence Gene Expression in Enterohemorrhagic Escherichia coli O157:H7