The virulence factors EAST1 and AIDA are often detected in ETEC/VTEC strains isolated from pigs and their role in diarrhoeal infections is discussed. In order to elucidate the pathogenesis of AIDA, the colonisation patterns of F4 positive and AIDA positive strains were investigated. Two wild-type Escherichia coli strains AIDA/EAST1 and F4/EAST1 isolated from diarrhoeal piglets were used for animal experiment to evaluate the ability of the EAST1 toxin to be involved in induction of diarrhoea. Gnotobiotic piglets were supplemented with normal porcine serum and orally inoculated with the strains. Faecal bacterial shedding of the challenge strains was observed during the experiment. Light microscopy and scanning electron microscopy were used to detect the colonisation pattern of both challenge strains. Although bacterial isolation demonstrated shedding of the challenge strains until the end of the experiment, diarrhoea did not develop in any piglet. Based on histological examination, piglets were more heavily colonised in the case of infection with E. coli O149/F4/EAST1 strain. Scanning electron microscopy showed bacterial cells of F4/EAST1 E. coli adhering to enterocytes, in contrast to AIDA/EAST1 which were poorly present on the intestinal surface. The EAST1 toxin alone was not able to induce diarrhoea in animals. Therefore our results demonstrate that the function/role of EAST1 and AIDA in colibacillosis of pigs remains to be elucidated.

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