Characterization of enteroaggregative Escherichia coli isolated from South Indian subjects in health and disease

Abstract

Objective: To characterize enteroaggregative Escherichia coli (EAEC) isolated from children and adults with different forms of diarrhoea, and also from controls. Design: A panel of 40 EAEC isolates from children with acute diarrhoea, adults affected in an epidemic of acute diarrhoea associated with EAEC and isolates from control children and adults were analyzed by adherence pattern, serotyping, DNA probing, haemagglutination, fluorescence actin staining (FAS), internalization:invasion and secretory activity in Ussing chambers in an attempt to distinguish isolates from symptomatic individuals from those obtained from asymptomatic excretors. Setting: A predominantly rural community of 95000 in South India kept under surveillance for diarrhoeal outbreaks. Results: Predominantly cellular adherence was seen in 27/40 (67.5%), adherence to glass in ten (25%) and a honeycomb pattern in three (7.5%). Of 40 isolates, 13 were rough and O untypable, and the remaining belonged to nine different O serogroups. Thirty-one isolates (77.5%) hybridized with the pCVD 432 probe. Erythrocytes from one or more of four species were agglutinated by 33 (82.5%) isolates. All isolates were negative in the FAS assay and a total of 17 (42.5%) isolates were internalized by HEp-2 cells at levels above 5%. In Ussing chamber experiments, an increase in short circuit current was seen with all ten isolates from patients affected by the outbreak and 14 of 20 other isolates from children with acute diarrhoea and controls. Conclusions: Characterization of EAEC from sporadic cases of diarrhoea and controls showed that they were a heterogeneous group of organisms, only some of which possess virulence factors such as toxin production and invasiveness. This differed from the isolates obtained from the diarrhoeal outbreak, which belonged to only two serotypes, had similar haemagglutination patterns and invasive ability.