HeLa cell adherence and cytotoxin production by enteropathogenic Escherichia coli isolated from infants with diarrhea in Thailand

Enteropathogenic Escherichia coli (EPEC) strains isolated from hospitalized infants with diarrhea in Thailand were examined for HeLa cell adherence and cytotoxin production. Of 101 strains examined, 56 adhered to HeLa cells in a localized pattern (LA), 27 adhered in a diffuse pattern (DA), and 18 did not adhere. All 56 LA EPEC strains were O:K serotype O119:K69. A total of 20 (83%) of 24 EPEC O86:K61 strains and 7 (38%) of 19 EPEC strains belonging to six other O:K serotypes exhibited DA. All LA EPEC strains hybridized with a DNA probe for genes encoding EPEC adherence factor, whereas none of the 27 DA or 18 nonadherent EPEC strains hybridized with EPEC adherence factor probe. Sonic extracts of 57 (58%) of 98 EPEC strains tested at a dilution of 1:100 caused greater than 25% mortality of HeLa cell monolayers. A total of 50 (88%) of 57 cytotoxic sonic extracts were inhibited to various degrees of 1:500 dilution of polyclonal rabbit antisera to purified Shiga toxin. The mean percent inhibition of cytotoxic sonic extracts by anti-Shiga toxin was 67% (range, 29 to 89%). Fifty percent (38 of 56) of LA EPEC strains, fifty-two percent (14 of 27) of DA EPEC strains, and fifty-three percent (8 of 15) of nonadherent EPEC strains produced Shiga-like toxins. Both adherence and low levels of cell-associated cytotoxins were identified in EPEC strains from Thailand, but there did not appear to be an association between these two factors.