Background and Aim: Worldwide phylogenetic analyses have demonstrated that virulent extra intestinal pathogenic Escherichia coli (ExPEC) strains belong mainly to group B2 and, to a lesser extent, to group D. On the contrary, most of the commensal strains are associated with group A or group B1. The most important members of ExPEC group are avian pathogenic E. coli (APEC), Uropathogenic E. coli (UPEC), and Mammary pathogenic E. coli (MPEC) which are responsible for extra intestinal diseases in animals or humans. This study tries to elucidate the status of mastitis causing E. coli strains as a member of ExPEC group and their relation to commensal E. coli isolates in terms of their phylogenetic groups. Methods: A total of 64 Escherichia coli isolates (mastitis causing isolates= 32, fecal isolates from the same cows= 32) were examined for determination of phylogroups using quadruplex PCR described by Clermont et al., 2013. Results: Most of the mastitis causing isolates belonged to the phylogroups A (43.75%) and B1 (40.62%), while 62.5% of fecal isolates were categorized as B1. The group C had the least members of both mastitis causing isolates (6.25%) and fecal isolates (3.12%). No members of the phylogroups D and E were detected among mastitis causing isolates and fecal isolates, respectively. Furthermore, among 32 paired samples, the phylogenetic groups of 12 paired samples (12 milk and 12 fecal samples from the same cows) were the same. Conclusion: The high prevalence of MPEC members in groups A and B1 may represent the commensal nature of these isolates.

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