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

Abstract

Healthy cattle are the primary reservoir for O157:H7 Shiga toxin-producing E. coli 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. coli O157:H7 outside the bovine gut. The E. coli 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. coli 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. coli MC2 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. 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, HCP pilus, FdeC adhesin) reflecting the capacity of the bacteria to colonize different segments of the bovine GIT. E. coli 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. coli 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°C. E. coli 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. coli 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. coli MC2 in the farm environment.

Aspartate metabolism is involved in the maintenance of enterohaemorrhagic Escherichia coli O157:H7 in bovine intestinal content

“…Because of the loss of viability of the E. coli commensal population after thawing of the BSIC samples (see the ‘Experimental procedures’ section), aspartate utilization was also analysed in a bovine commensal E. coli strain. The strain BG1, used as reference bovine commensal E. coli in previous studies (Bertin et al, , ; Segura et al, ) has been isolated from the small intestine of a cow at slaughter (Bertin et al, ). The whole genome of BG1 has been recently sequenced (Genbank accession number MOAH00000000) and analysed (Segura et al, ).…”

“…Furthermore, oxygen tension may fluctuate in the mammal intestine due to dynamic cycles of oxygen diffusion and oxygen consumption by facultative anaerobes and E. coli must rapidly respond to oxygen availability to survive in the mammal gut (Cole, 1996;Jones et al, 2007Jones et al, , 2011. In the absence of a suitable in vivo model, we designed in vitro growth conditions, corresponding to partial anaerobiosis, previously used in our laboratory to mimic the environment of the bovine small intestine (Bertin et al, 2011(Bertin et al, , 2013(Bertin et al, , 2014Segura et al, 2018). The bacterial suspensions were constituted by a mixture of bacteria, a part of them having access to oxygen while another part being under anaerobiosis, reflecting thereby the aeration conditions encountered in the mammalian small intestine.…”

“…The strain BG1, used as reference bovine commensal E. coli in previous studies (Bertin et al, 2011(Bertin et al, , 2013Segura et al, 2018) has been isolated from the small intestine of a cow at slaughter (Bertin et al, 2011). The whole genome of BG1 has been recently sequenced (Genbank accession number MOAH00000000) and analysed (Segura et al, 2017).…”

Plant species affects establishment ofEscherichia coliO157:H7gfp+on leafy vegetables

“…; Segura et al . ) and different diarrheagenic strains of E. coli might have different subsets of genes involved in binding or multiple mechanisms for binding to plant surfaces (Jeter and Matthysse ). We concluded that, for baby leaf spinach, rocket and Swiss chard, plant species, but not cultivar, affects colonization by E. coli O157:H7 gfp+ .…”

“…However, our model strain was Shiga toxin negative, the results of the present study need to be verified for Shiga toxigenic E. coli outbreak strains. Shiga toxin genes might be indirectly involved in intestinal colonization (Baines et al 2008;Segura et al 2018) and different diarrheagenic strains of E. coli might have different subsets of genes involved in binding or multiple mechanisms for binding to plant surfaces (Jeter and Matthysse 2005). We concluded that, for baby leaf spinach, rocket and Swiss chard, plant species, but not cultivar, affects colonization by E. coli O157:H7 gfp+.…”