Multidrug-Resistant Avian Pathogenic Escherichia coli Strains and Association of Their Virulence Genes in Bangladesh

Abstract

AbstractThe avian pathogenic Escherichia coli (APEC) strains are the chief etiology of avian colibacillosis worldwide. The present study investigated the circulating phylotypes, existence of virulence genes (VGs) and antimicrobial resistance (AMR) in 392 APEC isolates, obtained from 130 samples belonged to six farms using both phenotypic and PCR-based molecular approaches. Congo red binding (CRB) assay confirmed 174 APEC isolates which were segregated into 10, 9 and 8 distinctive genotypes by RAPD assay (discriminatory index, D=0.8707), BOX-PCR (D=0.8591) and ERIC-PCR (D=0.8371), respectively. The combination of three phylogenetic markers (chuA, yjaA and DNA fragment TspE4.C2) classified APEC isolates into B23 (37.36%), A1 (33.91%), D2 (11.49%), B22 (9.20%) and B1 (8.05%) phylotypes. Majority of the APEC isolates (75-100%) harbored VGs (ial, fimH, crl, papC and cjrC), and of them, VGs (papC and cjrC) and phylotypes (D2 and B2) of APEC had significant (p=0.004) association with colibacillosis. Phylogenetic analysis showed two distinct clades (Clade A and Clade B) of APEC where Clade A had 98-100.0% similarity with E. coli APEC O78 and E. coli EHEC strains, and Clade B had closest relationship with E. coli O169:H41 strain. Interestingly, phylogroups B2 and D2 were found in the APEC strains of both clades while the strains from phylogroups A1 and B1 were found in clade A only. In this study, 81.71% of the isolates were biofilm formers and possessed plasmids of varying ranges (1.0 to 54 kb). In vitro antibiogram profiling revealed that 100.0% isolates were resistant to ≥3 antibiotics, of which61.96%, 55.24, 53.85, 51.16 and 45.58 % isolates in phylotypes B1, D2, B22, B23 and A1, respectively were these antimicrobials. The resistance patterns varied among different phylotypes, notably in phylotype B22 showing the highest resistance to ampicillin (90.91%), nalidixic acid (90.11%), tetracycline (83.72%) and nitrofurantoin (65.12%). Correspondence analysis also showed significant correlation of phylotypes with CRB (p=0.008), biofilm formation (p=0.02), drug resistance (p=0.03) and VGs (p=0.06). This report demonstrated that B2 and A1 phylotypes are dominantly circulating APEC phylotypes in Bangladesh; however, B2 and D2 are strongly associated with the pathogenicity. A high prevalence of antibiotic resistant APEC strains from different phylotypes suggest to use of organic antimicrobial compounds, and/or metals, and the rotational use of antibiotics in the poultry farms in Bangladesh.