Types of Enteropathic E.coli

Many primary bacterial enteropathogens have been implicated as a cause of gastrointestinal disease in dogs and cats. Particular attention has been focussed on Salmonella sp. and Campylobacter sp. as these can readily be identified by selective culture. However, it is now clear that E.coli can also be important, as the molecular detection of genes encoding pathogenicity by PCR can distinguish enteropathic E.coli from harmless strains which are commonly present in the faeces.

Enteropathogenic E.coli (EPEC) appear to be the most common type of pathogenic E.coli and can cause both acute and chronic diarrhoea. They work by an “attaching-effacing” mechanism that strips microvilli from enterocytes resulting in osmotic diarrhoea due to compromised absorptive function, illustrated here:

Cytotoxin – secreting E.coli secrete cytotoxins which are lethal to intestinal epithelial cells, causing haemorrhage and ulceration, potentially mimicking the severe enterocolitis caused by invasive bacteria. Enterohaemorrhagic E.coli (EHEC, VTEC) are the best known in this group, which also includes enteroaggregative E.coli (EAEC) and CNF-secreting E.coli.

Enterohaemorrhagic E.coli secrete these toxins in addition to causing attaching-effacement of microvilli like EPEC.

Enteroinvasive E.coli (EIEC) can invade the mucosa of the distal small bowel and colon causing acute enterocolitis. This is typically manifest as diarrhoea accompanied by passage of blood and mucus, and may result in a potentially fatal septicemia if the organisms penetrate the intestinal barrier.

Enterotoxigenic E.coli (ETEC) do not cause intestinal damage, but secrete toxins which have a specific biochemical effect. These act as secretagogues resulting in a watery electrolyte-rich diarrhoea.

All of these pathogenic E.coli can cause acute clinical disease. However, properties such as adherence to the surface by EPEC or invasion of the mucosa can promote long-term colonisation predisposing to chronic disease or carrier status. The outcome also depends on host reaction, particularly the ability to mount an effective immune response.

Management of Enteropathic E.coli

Treatment of enteric pathogens with antibiotics should be considered for severe or chronic clinical disease, and when there is evidence of septicaemia or endotoxaemia. The choice should be guided by antibiotic sensitivity testing. Chronic cases can be difficult to manage and this may be due to a number of factors including poor support from a defective host response, antibiotic resistance, or re-infection from the environment.

An oral autogenous E.coli vaccine prepared from pathogenic E.coli isolated from that individual dog or cat should be considered as an adjunct to treatment particularly to help prevent recolonisation. This approach has been shown to be particularly effective even in the challenging environment of breeding and boarding kennels.