A study on some phenotypic virulence markers of enteropathogenic Escherichia coli

The problem of enteropathogenic Escherichia coli (EPEC) causing diarrhoea in infants exists in India. But often the enteropathogenic status is not based on adequate characterization. Hence there is a need for evaluating the serotyping being used to identify EPEC for its validity in the light of recent knowledge on phenotypic markers of virulence. This study was done to evaluate the EPEC isolates for two potential virulence factors namely entero-adhesiveness with subsequent actin accumulation and verotoxin production.

Fifty consecutive EPEC strains identified by serotyping from stool samples of children with diarrhoea during January 1997 to June 1999 were studied for HEp-2 cell adherence, the fluorescent actin staining (FAS) characteristics of Hep-2 cells and vero cytotoxin production.

Serotypes O55, O125 and O126 accounted for most of the isolates. In the Hep-2 assay, 72 per cent of the strains showed localised pattern of adherence and 22 per cent showed a mixed pattern of localised and diffuse adherence. In the FAS test 96 per cent strains showed typical staining while none of the strains produced verotoxin.

'O' serogrouping appears to be still the simplest and an useful test for presumptive identification of EPEC. The FAS test for confirmation of EPEC was found to be very consistent in indicating EPEC.