Escherichia coli (E. coli) is the most important of the gram-negative bacteria family Enterobacteriaceae. The bacterium is found in the normal gut flora of humans, mammals and birds. Under normal circumstances it accounts for only a small proportion – up to one per cent – of the microflora. E. coli is an indicator of faecal contamination and is widespread in the environment. E. coli is very resistant to environmental influences and is able to grow in dry faeces for months.
There are non-pathogenic and pathogenic E. coli strains. While non-pathogenic strains do not cause disease but contribute to the health of the intestinal tract, pathogenic strains cause a variety of clinical signs. Pathogenic strains differ from non-pathogenic by the presence of virulence factors. These virulence factors are responsible for the particular disease observed. They possess specific fimbriae (e.g. F4, F18), hair-like extensions, that are responsible for the attachment ( adhesion ) to certain types of gut epithelial cells. The formation, for example, of heat-sensitive toxin (LT) or heat-resistant toxin (ST) determines the virulence of the bacteria. An interaction between different virulence factors can give the clinical picture of colibacillosis. Colibacillosis has great impact in the early and late suckling phase. The piglets get infected with E. coli orally from the environment. The first source of infection is most often the sow. In addition, faeces from sick pen-mates increases the bacterial load massively. The first cases of diarrhoea can be seen just a few hours after infection. Contaminated, moist pens and compartments also increase the bacterial load. Because of its high prevalence, E. coli is, from an economic perspective, one of the most significant pathogens causing diarrhoea. E. coli strains with fimbriae types F4 and F18 play the most important role. Recently there have been more reports of diarrhoea from 14 days onwards caused by E. coli.