Differential gene expression and adherence of Escherichia coli O157:H7 in vitro and in ligated pig intestines. PLoS ONE 6: e17424. Supporting information Additional supporting information may be found in the online version of this article at the publisher

Background: Escherichia coli O157:H7 strain 86–24 grown in MacConkey broth (MB) shows almost no adherence to cultured epithelial cells but adheres well in pig ligated intestines. This study investigated the mechanisms associated with the difference between in-vitro and in-vivo adherence of the MB culture. Methodology/Principal Findings: It was found that decreased adherence in vitro by bacteria grown in MB was mainly due to lactose, possibly implicating the involvement of carbon catabolite repression (CCR). Expression of selected virulence-related genes associated with adherence and CCR was then examined by quantitative PCR. When bacteria were grown in MB and Brain Heart Infusion with NaHCO3 (BHIN) plus lactose, pH was reduced to 5.5–5.9 and there was a significant decrease in expression of the locus of enterocyte effacement (LEE) genes eae, tir, espD, grlA/R and ler, and an increase in cya (cAMP), and two negative regulators of the LEE, gadE and hfq. Putative virulence genes stcE, hlyA, ent and nleA were also decreased in vitro. Reversal of these changes was noted for bacteria recovered from the intestine, where transcripts for qseF and fis and putative virulence factors AidA15, TerC and Ent/EspL2 were significantly increased, and transcripts for AIDA48, Iha, UreC, Efa1A, Efa1B, ToxB, EhxA, StcE, NleA and NleB were expressed at high levels. Conclusions/Significance: Presence of lactose resulted in decreased expression of LEE genes and the failure of EHEC O157:H7 to adhere to epithelial cells in vitro but this repression was overcome in vivo. CCR and/or acidic pH may hav