Virulence genes, serobiotypes and antibiotic resistance profile of Escherichia coli strains isolated from aquaculture and other sources

In order to determine the prevalence of pathogenic Escherichia coli, a total number of 155 E. coli isolates from aquaculture, clinical and veterinary sources were screened for seven pathogenic virulence markers and a house-keeping gene by a polymerase chain reaction. The targeted virulence genes included eaeA of enteropathogenic E. coli, elt and est of enterotoxigenic E. coli (ETEC), ipaH of enteroinvasive E. coli, pCVD432 of enteroaggregative E. coli, stx, hlyA and eaeA of shigatoxigenic E. coli (STEC) and Enterohaemorrhagic E. coli. All the isolates were positive for phoA, the house-keeping gene for E. coli. Among the 155 isolates, seven numbers (4.5%) harboured the virulence markers belonging to the pathogenic group ETEC and STEC. The virulent genes detected in these groups were elt, est, hlyA and stx. The sources of these virulence genes were fish (hlyA), shrimp (elt), feeder canal water (hlyA and elt) of aquaculture origin and from diarrhoea affected cow (hlyA, est and stx). The isolates with pathogenic traits belonged to the serogroups O6 or O29 and the remaining could not be typed. They showed resistance to two to four antibiotics out of the 12 antibiotics tested. Biotyping revealed that three isolates belonged to a single biotype (7333) and the remaining isolates were of diverse types. In conclusion, a molecular tool such as PCR proves as more effective tool for detection of this pathogen than the conventional methods. Detection of these emerging pathogens in aquaculture samples warrants for strict adherence to hygienic handling at retail outlets and proper cooking by the consumer before consumption.