ABSTRACT
E. coli are Gram-negative, motile (most isolates), facultative anaerobic, rod-shaped bacteria. Strains of pathogenic E. coli associated with gastrointestinal infection can be categorized on the basis of colonization and virulence mechanisms into specific pathotypes (Doyle and Padhye, 1989). Enteroinvasive E. coli (EIEC) and Enteroaggregative E. coli (EAEC) can cause diarrhoea, but both types of E. coli are host-restricted to humans and have not been observed in other animals. Enterotoxigenic E. coli (ETEC) is one of the most common causes of diarrhoea in humans, and this toxin-producing type of bacteria can also cause disease in other animals. Enteropathogenic E. coli (EPEC) can tightly colonize the intestinal epithelium and deform the colonized epithelial cell, and this ‘attaching and effacing’ can result in diarrhoea in the host. Strains of both ETEC and EPEC are observed in cattle, particularly in calves, but the specific role these pathotypes may play in cattle disease is controversial (Kolenda et al., 2015). Enterohaemorrhagic E. coli (EHEC) is a pathotype with colonization mechanisms similar to EPEC, but EHEC strains also harbour genes that produce shiga toxins, also known as vero toxins (Smith et al., 2014). Production of shiga toxins is associated with severe illnesses in infected humans and the toxin genes are found in a variety of E. coli strains. However, the most common disease-causing shigatoxigenic E. coli (STEC) are the strains characterized as EHEC.
