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Type strains of enteroaggregative Escherichia coliEAEC (17-2, serotype O3:H2; JM 221, serotype O92:H33), isolates from an adult and a child with diarrhoea and an asymptomatic colonised child were used to orally infect adult rabbits. The experimental animals were followed up and sacrificed at defined time periods. Colonisation of both small and large intestine was seen with all strains and isolates used. Isolates from an adult patient with diarrhoea (MP 27) and from an asymptomatic colonised child from the community (KM 1337) were recovered from the small intestine during the first week of infection and subsequently from the large intestine. A total of seven rabbits was infected with MP 27; while colonising the gastrointestinal tract of all seven rabbits, this isolate caused diarrhoea in only one. On ultrastructural examination, the rabbits infected with 17-2 showed invasion of lymphoid follicles. Bacteria were seen in intercellular spaces and within M cells, a finding that has not previously been described. It is clearly possible to produce gut colonisation by oral infection with EAEC in adult rabbits with normal flora.

For detailed etiological studies we isolated invasive enteric bacterial pathogens in 16, non-invasive pathogens in 13 and no pathogens in 11 of 40 adults with untreated acute diarrhea of less than 5 days duration at a tertiary care hospital in southern India. It was possible to establish a system for the objective assessment of the clinical severity of illness. Hemorrhage in the rectal mucosal lamina propria, especially pericryptal, was a striking feature in rectal biopsies. This was associated with a vascular lesion with endothelial damage. The prevalence of the vascular lesion did not correlate with the etiological agents or the severity of the histological abnormality in the rectal mucosa. However, there was a good correlation between the presence of vascular abnormalities and clinical severity. While the vascular changes could be the result of non-specific trauma to the rectal mucosa due to diarrhea, it is suggested that they may have an as yet unknown role in determining clinical severity.