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

Audrey Segura, Pauline Auffret, Delphine Bibbal, Marine Bertoni, Alexandra Durand, Grégory Jubelin, Monique Kérourédan, Hubert Brugère, Yolande Bertin, Evelyne Forano

Healthy cattle are the primary reservoir for O157:H7 Shiga toxin-producingE. coliresponsible 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 ofE. coliO157:H7 outside the bovine gut. TheE. coliO157: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 ofE. coliMC2 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. coliMC2 survived in rumen fluids, grew in the content of posterior digestive compartments and survived in bovine feces at 15°C predicting a successful transit of the bacteria along the bovine GIT and its persistence outside the bovine intestine.E. coliMC2 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, HCP pilus, FdeC adhesin) reflecting the capacity of the bacteria to colonize different segments of the bovine GIT.E. coliMC2 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 commensalE. colistrain BG1. Furthermore, in contrast to BG1,E. coliMC2 responded to temperature stresses by inducing the genescspAandhtrAduring its survival in bovine feces at 15°C.E. coliMC2 also activated genes that are part of the GhoT/GhoS, HicA/HicB and EcnB/EcnA toxin/antitoxin systems involved in the response ofE. colito 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 ofE. coliMC2 in the farm environment.