Development of a capture/enrichment sandwich ELISA for the rapid detection of enteropathogenic and enterohaemorrhagic Escherichia coli O26 strains

Aims: To improve the sensitivity of a monoclonal antibody (MAb 2F3) based enteropathogenic Escherichia coli (EPEC)/enterohaemorrhagic E. coli ( EHEC) serogroup O26-specific sandwich ELISA (sELISA), using a capture/enrichment format of the assay. Methods and Results: The sELISA utilized an EPEC/EHEC O26-specific MAb 2F3 as the capture reagent and an E. coli serogroup O26 lipopolysaccharide-specific polyclonal antibody in the development stage. Wells containing faeces test samples from bovine enteritis cases and agar colony sweep cultures from human diarrhoea cases, after a 2-h capture stage, were washed and enrichment of the captured cells was encouraged by addition of tryptone soya broth. After overnight incubation, the contents of each well were transferred to sterile wells and the sELISA completed. Any sELISA positive samples were then subcultured onto blood agar to recover and further characterize the positive cultures. The assay had a sensitivity of 10(3) CFU ml(-1). ELISA positive samples consisted of 21 (4.8%) of the 442 bovine and 19 (3.7%) of the 519 human samples tested, and ELISA positive EPEC/EHEC O26 strains were isolated from 11 and three of these samples respectively. Conclusion: The capture/ enrichment method improved the sensitivity of a MAb-based sELISA for the detection of EPEC/EHEC O26 strains, and also contributed to an improved isolation rate of the organism from field samples. Significance and Impact of the Study: The application of a specific MAb in a capture/ enrichment format of the sELISA, provides a prospectively suitable screening method for the detection of pathogenic bacteria from mixed culture samples.