Nine Escherichia coli shiga-toxin producing (STEC), human enteropathogenic (EPEC) isolates were subjected to RAPD-PCR using three universal primers; primers 4, 5, and 6, to study their heterogeneity. Primer 6 was the most successful in developing heterobands for most of the investigated isolates and resulted in six clades. Primer 6 highly discriminated three of the most virulent isolates; isolates 7, 8, and 5. Primer 4 ranked the second successful primer, fortunately it placed the fourth most virulent isolate, isolate 6, into a separate clade with a high linkage distance of 3.9 separating it from the rest of the isolates. None of the investigated primers developed heterobands for the isolates 1, 2, and 3 which were always treated as one with zero Euclidean linkage distance among them. Primer 6 RAPD-PCR patterns for isolates 7, 8, and 5 as well as primer 4 RAPD-PCR pattern for isolate 6 could be regarded as reference patterns for the direct detection of such isolates and other related ones especially in Al-Kharj district. Additionally, heterobands of the most virulent isolates, in further investigations, could be studied to be used as markers for the detection of virulent EPEC, STEC isolates.

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