Distribution of virulence related genes among enteroaggregative Escherichia coli isolates: using multiplex PCR and hybridization.

The importance of enteroaggregative Escherichia coli (EAEC) strains in public health around the world is becoming increasingly clear. EAEC diagnosis has long been problematic. In this study, the recently designed multiplex PCR based on three plasmid-borne genes (AA probe, aap, and aggR) and DNA hybridization assay with plasmid-derived DNA probes were used for detection of HEp-2 adherent strains. These were isolated from an epidemiologic study of diarrhea in Iran. Using AA and DA probes revealed that 32.4%, 16.2%, 23%, and 28.4% of these isolates were AA, DA, AA/DA, and non-AA/DA, respectively. However, employing multiplex PCR for detection of these isolates, showed that 51.3% of the strains were AA and the rest 48.7% were not AA. While presence of other genes (pet, shf, aggA, aafA) considered to be specific for EAEC were checked among these isolates. The data obtained revealed that except for AA, aap, and aggR, the rest of the virulence related genes are not specific for EAEC isolates and are randomly distributed among adherent isolates. Over all the results obtained here indicated that this multiplex PCR is specific and sensitive assay. Phenotypically adherent strains are divided into two main groups, by use of this multiplex PCR i.e., typical EAEC isolates that carry the three plasmid-borne genes all together and atypical EAEC isolates in which the three genes are not linked together.