Factors Involved in the Persistence of a Shiga Toxin-Producing Escherichia coil O157:H7 Strain in Bovine Feces and Gastro-Intestinal Content

Healthy cattle are the primary reservoir for O157:H7 Shiga toxin-producing E coil responsible for human food-borne infections. Because farm environment acts as a source of cattle contamination, it is important to better understand the factors controlling the persistence of E. coil O157:H7 outside the bovine gut. The E. coil O157:H7 strain MC2, identified as a persistent strain in French farms, possessed the characteristics required to cause human infections and genetic markers associated with clinical O157:H7 isolates. Therefore, the capacity of E. coil MC2 to survive during its transit through the bovine gastro-intestinal tract (GIT) and to respond to stresses potentially encountered in extra intestinal environments was analyzed. E. coil MC2 survived in rumen fluids, grew in the content of posterior digestive compartments and survived in bovine feces at 151 degrees C predicting a successful transit of the bacteria along the bovine GIT and its persistence outside the bovine intestine. E coli MC2 possessed the genetic information encoding 14 adherence systems including adhesins with properties related to colonization of the bovine intestine (F9 fimbriae, EhaA and EspP autotransporters, HOP pilus, FdeC adhesin) reflecting the capacity of the bacteria to colonize different segments of the bovine GIT. E coil MC2 was also a strong biofilm producer when incubated in fecal samples at low temperature and had a greater ability to form biofilms than the bovine commensal E. coil strain BG1. Furthermore, in contrast to BG1, E. coli MC2 responded to temperature stresses by inducing the genes cspA and htrA during its survival in bovine feces at 15 degrees C. E coil MC2 also activated genes that are part of the GhoT/GhoS, HicA/HicB and EcnB/EcnA toxin/antitoxin systems involved in the response of E. coil to nutrient starvation and chemical stresses. In summary, the large number of colonization factors known to bind to intestinal epithelium and to biotic or abiotic surfaces, the capacity to produce biofilms and to activate stress fitness genes in bovine feces could explain the persistence of E. coil MC2 in the farm environment.