Adherence and associated virulence gene expression in acid-treated Escherichia coli O157 : H7 in vitro and in ligated pig intestine.

ABSTRACT

Escherichia coli O157 H7 cells that interact with intestinal epithelial cells in animals and humans do so after passage through the low pH of the stomach. This study compared adherence and its associated virulence gene expression in acid-treated (AT) and non-acid treated (NAT) E. coli O157 H7 strain 86-24 in vitro and in ligated pig intestine. It was found that in vitro, AT O157 H7 had significantly decreased adherence accompanied by decreased expression of stcE and toxB but not of the locus of enterocyte effacement (LEE) genes. Expression of gadE, genes involved in quorum sensing, and the global regulators cyaA, hfq, lrp, fis and himA was significantly increased; notably, ureD expression was increased 29-fold compared with NAT O157 H7. AT O157 H7 colonized the pig intestine as effectively as NAT O157 H7 bacteria. Expression of 70 of 72 virulence genes from bacteria recovered from the intestine was similar between AT and NAT O157 H7, except ureD, pagC and bax, whose level of expression was reduced in the AT bacteria. Genes involved in acid response, regulators gadE, cyaA and hfq, and toxin synthesis genes (stx2A and stx2B) were expressed at significantly reduced levels in the intestine by both AT and NAT strains. Expression in the intestine of the LEE and putative adhesion factors cahA, iha and lpf2 was at levels similar to those in vitro, while ehaA and ureD in NAT O157 H7 were expressed significantly more highly in vivo than in vitro. These data indicate that AT and NAT O157 H7 behave differently, and that expression of their virulence genes is regulated differently in vitro from in vivo.