Responses of Cattle to Gastrointestinal Colonization by Escherichia coli O157:H7

Abstract

Recent research has established that the terminal rectum is the predominant colonization site of enterohemorrhagic Escherichia coli O157:H7 in cattle. The main aim of the present work was to investigate pathological changes and associated immune responses at this site in animals colonized with E. coli O157:H7. Tissue and gastrointestinal samples from a total of 22 weaned Holstein-cross calves challenged with E. coli O157:H7 were analyzed for bacterial colonization and pathology. Five unexposed age-matched calves were used as comparative negative controls. E. coli O157:H7 bacteria induced histopathological alterations of the rectal mucosa with enterocyte remodeling. This was often associated with removal of the colonized epithelial layer. Immunogold labeling and transmission electron microscopy (TEM) showed E. coli O157 bacteria on pedestals, as part of attaching and effacing lesions. These pathological changes induced a local infiltration of neutrophils that was quantified as larger in infected animals. Rectal mucosal immunoglobulin A responses were detected against the E. coli O157:H7 antigen. This work presents evidence that E. coli O157:H7 is not a commensal bacteria in the bovine host and that the mucosal damage produced by E. coli O157:H7 colonization of the terminal rectum induces a quantifiable innate immune response and production of specific mucosal antibodies.Enterohemorrhagic Escherichia coli (EHEC) infection has emerged in the last 20 years as a cause of diarrhea that can lead to the more serious consequence of hemolytic-uremic syndrome and thrombotic microangiopathy. The majority of EHEC infections are caused by E. coli O157:H7 (24), and this serotype has been isolated frequently from cattle feces. Many human EHEC O157 infections originate, either directly or indirectly, from exposure to cattle feces (17), and a key step in protecting humans from EHEC infection is to understand and control E. coli O157:H7 colonization of cattle.Experimental challenges have suggested a variety of colonization sites in cattle (4,5,12). However, more recently, the terminal rectal mucosa has been identified as the major site of E. coli O157:H7 colonization (25), and this finding has been confirmed in slaughter animals (20). From an understanding of where E. coli O157:H7 colonizes the bovine intestinal tract, there is an opportunity to examine pathological changes at the site and to determine whether these changes correlate with the development of immunological responses. The main aim of the research is to underpin methods to control this pathogen in its main animal reservoir.A feature of E. coli O157:H7 infection is the formation of attaching and effacing (A/E) lesions, characterized by the elimination of the microvilli and intimate enterocyte attachment (7, 16). In vivo, A/E lesions are present at the terminal rectum of naturally and experimentally infected cattle, and inactivation of the type III secretion apparatus that is essential for this phenotype prevents E. coli O157:H7 colonization of cattle (27). The profound...

Strain-Dependent Cellular Immune Responses in Cattle following Escherichia coli O157:H7 Colonization

“…This is significant, because TNF-␣ is upregulated during C. rodentium colonization in mice (77), while pretreatment of bovine colonic explants with TNF-␣ has been shown to upregulate mucin secretion and reduce EHEC O157:H7 colonization (78). The observation that TNF-␣ is not induced at the terminal rectum would imply that this pathway is not active in vivo and is likely to contribute to the difference between the pathogenicity of C. rodentium in mice, which results in weight loss, moderate mortality, and colonic hyperplasia (79,80), and that of EHEC O157:H7 in cattle, where the infection is asymptomatic and demonstrates only a mild neutrophilic infiltrate, suggesting that while immunogenic, colonization is not a major inflammatory event (42).…”

“…However, to our knowledge, only two studies have considered the role of cellular immunity during EHEC O157:H7 colonization in ruminants; these identified lymphoproliferative cellular responses to heat-killed EHEC O157:H7 (40) and recombinant antigens (41) in bovine peripheral blood mononuclear cells and ovine rectal lymph node cells, respectively. The case for a protective cellular immune response is further strengthened by the observations that colonized bovine epithelial cells are exfoliated in vivo (42) and that some strains are efficiently internalized by bovine epithelial cells both in vivo and in vitro (43).…”

Escherichia coli O157:H7 Strain Origin, Lineage, and Shiga Toxin 2 Expression Affect Colonization of Cattle

“…Mature cattle are considered the primary reservoir for E. coli O157:H7 and historically were reported to have no symptoms or pathologies (17,23,38); this was attributed both to a lack of receptors for a critical E. coli O157:H7 virulence factor, Shiga toxin 1 (Stx1 [29]), and to a differential expression of type III protein secretion system effector molecules such as EspA, EspD, and Iha (25,30) in cattle compared to humans. In 2008, it was established for the first time that E. coli O157:H7 causes mild to severe intestinal pathology in persistent shedding cattle (5,26) and that the secreted cytotoxins enhanced E. coli O157:H7 colonization of intestinal tissues of cattle (6). This suggested that cattle were susceptible to E. coli O157:H7 infection and that previously discounted virulence factors could influence the amount of colonization in cattle.…”

Insights into mucosal innate responses to Escherichia coli O157 : H7 colonization of cattle by mathematical modelling of excretion dynamics

“…Our previous research has demonstrated an influx of neutrophils associated with an inflammatory response in the terminal rectal mucosa of cattle colonized by EHEC O157 : H7 at day 14 onwards following oral or rectal challenge [35]. As exemplified by the model, the earlier induction of the innate response is the key battleground affecting persistence and explains the selection of these effector proteins.…”

“…Both of these processes have a biological basis and it is likely that both may contribute to the second peak. It is evident from histology carried out on rectal tissue from colonized animals that infection does lead to detachment of the affected epithelial cells [35]. Given the single infection dose and the limited colonization site, it is proposed that this detachment occurs over a defined enough time period to significantly increase bacterial numbers in the rectal mucus.…”