Faeces from urban children > 2 years old with acute diarrhoeal illness and from non-diarrhoeal infants (controls) were examined for and other enteropathogens. A total of 990 isolates from 100 patients and 50 controls was tested for enteropathogenic (EPEC) serotype (O:H), adherence to HEp-2 cells after incubation for 3 and 6 h, fluorescent actin staining (FAS), DNA hybridisation with EAF, , STh, STp and EAggEC probes and production of heat-labile enterotoxin (LT) and verocytotoxin (VT) with Y1 and Vero cells. EPEC were the most prevalent enteropathogens in patients (32.7%; and 14% in controls). Enteroinvasive (EIEC) and Vero cytotoxin-producing (VTEC) were not detected. The rate of isolation of enterotoxigenic (ETEC) was identical in both groups. Among the EPEC isolates the prevalent serotypes were O111:H2, O55:NM and O119:H6. Localised adherence (LA) was found significantly more frequently in isolates from patients (19.6%) than controls (2.1%). All LA-positive EPEC isolates were FAS+ and +, but only 75.2% of them hybridised with the EAF probe. Diffusely adhering (DAEC) and enteroaggregative (EAggEC) were found with equal frequency in patients and controls. Twenty-seven isolates were negative for EAF but positive for and FAS and produced LA in 6-h adherence tests. These EAF-/+ strains were the only putative enteropathogen identified in seven patients and were not found in controls. The ability of these strains to elicit ultrastructural cell alterations and cell-signalling events was evaluated in Caco-2 cells (human colon carcinoma cell line) by the gentamicin invasion assay and by transmission electron microscopy. The numbers of intracellular bacteria in cell invasion tests varied from 0.4% to 1.6% of the cell-associated bacteria after a 6-h incubation period. Tyrosine phosphorylation of host cell proteins was assessed in HEp-2 cells by immunofluorescence microscopy and all strains gave positive results. EAF-/+ strains express most of the virulence properties found among true EPEC strains and can be a relevant cause of infant diarrhoea in developing countries.


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