Extraintestinal pathogenic Escherichia coli (ExPEC) is one of the most common bacterial pathogens, which causes costly health problems encountered by humans at all ages [1]. ExPEC causes asymptomatic bacteriuria, cystitis, pyelonephritis, and catheter-associated urinary tract infections (UTIs) [2], [3]. UTIs are caused by the ExPEC known as the uropathogenic E. coli (UPEC) strains usually derived from the normal intestinal microflora [4], [5]. Antimicrobial therapy is often required for treating UTIs caused by UPEC strains. However, recently, antibiotic resistance in uropathogenic bacteria, especially UPEC strains, has become a serious health concern worldwide, especially in developing countries, such as Iran [6], [7], [8], [9], [10], [11], [12]. Resistance to commonly used antibiotics is increasing; however, patterns of resistance are different in terms of phylogenetic groups, virulence factors, geographic locations, and patient characteristics [13]. Among the tools for studying the population genetics of ExPEC strains, triplex polymerase chain reaction (PCR) has been widely used for its rapidity and simplicity [14]. This phylogenetic method showed that pathogenic and commensal strains of E. coli have been categorized into four main phylogenetic sets of A, B1, B2, and D, which are predominant in human and animal populations. Virulent strains of human ExPEC are frequently classified into the B2 or D phylogroups, whereas commensal strains and less virulent strains belong mostly to the A or B1 group [15], [16]. The strains of the four phylogenetic groups have various phenotypic features, including their ability to use different sugars, antibiotic resistance profiles, and temperature relationships with their growth rates. With a combination of the three genetic markers, including chuA, yjaA, and DNA fragment TspE4.C2, these phylogenetic groups can be divided into seven subgroups of A0, A1, B1, B22, B23, D1, and D2, which increase the discrimination power of ExPEC population analysis [17]. In 2013, Clermont et al. have modified the triplex PCR method by adding a further gene target, arpA, thus making the new method a quadruplex PCR. The entry of the arpA gene enables strains belonging to the F phylogroup, formerly misidentified as D strains, to be distinguished because except for the strains belonging to the B2 and F phylogroups, arpA is present in all E. coli. This method enables an E. coli isolate to be assigned to one of the eight phylogroups, including A, B1, B2, C, D, E, and F, belonging to E. coli sensu stricto, whereas the eighth is the Escherichia cryptic clade I [18]. Increasing antimicrobial resistance among ExPEC strains, especially UPEC isolates, and horizontal genetic transfer mechanism allows the exchange of resistance genes among phylogroups, which may increase the emergence of resistant strains belonging to commensal strains [19]. Consequently, characterizing the clonal structure within phylogenetic groups and its association with antibiotic resistance profiles is important. Although some studies of antibiotic resistance profiles of UPEC strains were conducted in Iran, the antibiotic resistance pattern and phylogenetic groups and subgroups are less considered. Therefore, this study was designed to consider the antibiotic resistance profile, phylogenetic group, and subgroup analyses in ExPEC strains isolated from hospitalized patients in north Iran.