Characterization of Escherichia coli Isolates from Commercial Layer Hens with Salpingitis

Problem statement: Escherichia coli isolates are the most common bacterial agents of salpingitis in commercial layer hens. The objectives of this study were to determine the phylogenetic groups/subgroups and antibiotic resistance of E. coli isolates from salpingitis cases in commercial layer hens farms in southeast of Iran. Approach: One hundred twenty one E. coli isolates from oviducts of layer hens with salpingitis were examined to determine their O-serogroup, phylogenetic group/subgroup and antibiotic resistance pattern. Results: O-serogroup determination test showed that 47 (38.84%) isolates were typeable and belonged to eleven different O serogroups including: O1, O2, O6, O8, O15, O20, O25, O36, O78, O86 and O111 and 71 (58.67%) isolates were O-nontypeable. Three most prevalent serogroup were O78, O2 and O1 respectively. PCR assays showed that the isolates fall into four phylogenetic groups A (41.32%), D (33.88%), B2 (14.87%) and B1 (9.91%). Ninety nine (81.81%) isolates fell into six phylogenetic subgroups including: A₀ (17.35%), A₁ (23.96%), B2₂ (5.78%), B2₃ (9.09%), D₁ (13.22%) and D₂ (20.66%). All of the E. coli isolates from O78 serogroup belonged to A phylo-group whereas the O2 isolates mostly fell into D group. The maximum antibiotic resistance was against tetracycline (100%) and minimum resistance was against linco-spectin (37.19%). Twenty four isolates (19.83%) were resistant to all of the examined antibiotics. Twenty three different patterns of multiple drug resistance were observed, out of which N-Te-Sxt-Fm- Nfx-C and N-Te-Sxt-Gm-Fm-Nfx-C-Ls was the two most frequent patterns respectively. The resistant isolates were found in all of the phylogenetic groups and or sub groups. Conclusion: There are similarities between salpingitis derived E. coli strains and other avian pathogenic E. coli isolates in phylogroups, O-serogroups and antibio-resistance patterns.