In the present study, 100 Avian-Pathogenic Escherichia coli (APEC) isolates from colibacillosis-suspected broilers and 100 Avian Faecal Escherichia coli (AFEC) isolates from healthy broilers in Iran were examined by PCR for confirmation of their serogroups and phylogenetic background, and their association with ten virulence-associated genes (VAG) including fimC, iutA, chuA, sitA, iss, cvaA/B, hylA, stx1, stx2, and yjaA. Serogroups O78, O1, O2 and O18 were the prominent strains including 54 % of the APEC and 23 % of the AFEC strains. At phylotyping, the majority of APEC strains belonged to phylogenetic group E (22 %) while for the AFEC strains, half of the isolates were not assigned to any group but the predominant phylogroup was E (27 %). Virulence genotyping, revealed that the predominant VAGs were iutA (97 %), fimC (87 %) and iss (84 %) among APEC strains, and fimC (95 %), iss (93 %) and sitA (87 %) in AFEC strains. This is the first time that phylogroup E is described as predominant phylogroup among APEC strains also, this is the first report on the presence of the stx1 gene in APEC strains isolated from broilers in Iran. The results of the present study indicate that VAGs are more prevalent in APEC strains belonging to O2 and O78 serogroups, also phylogroups E and D have more frequency of VAGs than other phylogroups. Therefore, the APEC strains belonging to O2 and O78 serogroups and phylogroups E and D probably have more pathogenicity to broilers.

在本研究中，通过PCR检查了100例怀疑是大肠杆菌病的肉鸡的禽致病性大肠杆菌（APEC）分离株和100例健康伊朗肉鸡的100禽粪便大肠杆菌（AFEC）分离株，以确认其血清型和系统发生背景，以及与十种毒力相关基因（VAG）相关，包括fimC，iutA，chuA，sitA，iss，cvaA / B，hylA，stx1，stx2和yjaA。O78，O1，O2和O18血清群是主要菌株，包括54％的APEC和23％的AFEC菌株。进行系统分型时，大多数APEC菌株属于系统发生E组（22％），而对于AFEC菌株，一半的分离株未归入任何组，但主要的系统组为E（27％）。毒力基因分型显示，APEC菌株中主要的VAGs为iutA（97％），fimC（87％）和iss（84％），以及AFEC中的fimC（95％），iss（93％）和sitA（87％）株。这也是首次将phylogroup E描述为APEC菌株中的主要phylogroup，这是有关stx1存在的首次报道。从伊朗肉鸡中分离出的APEC菌株中的基因。本研究的结果表明，VAGs在属于O2和O78血清群的APEC菌株中更为普遍，系统群E和D的VAGs频率也高于其他系统群。因此，属于O2和O78血清群以及E和D的系统群的APEC菌株可能对肉鸡具有更大的致病性。