Molecular characterization, antibiotic susceptibility and phage sensitivity of Avian Pathogenic Escherichia coli isolated from colibacillosis cases
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Avian Pathogenic Escherichia coli (APEC) cause extra-intestinal infections collectively known as colibacillosis, which result into significant economic losses for the poultry industry. The aim of this study was to characterize the prevailing Avian Pathogenic E. coli isolates and establish stocks of APEC lytic bacteriophages, for future development of cocktail products as alternatives to antibiotics in the management of avian colibacillosis. Fifty-six (56) glycerol stocks of Escherichia coli isolates obtained from chicken that had died of colibacillosis were analyzed for virulence, serogroup, phylogroup, antimicrobial susceptibility, and sensitivity to lytic phages. Escherichia coli characterization was done through phenotypic and multiplex PCR methods whereas antimicrobial susceptibility was done by Disk-diffusion method. Bacteriophage isolation and preliminary characterization was achieved using the spot assay and overlay plating techniques. All the 56 (100%) APEC isolates were resistant to at least one antibiotic while 50 (89.3%) isolates were resistant to at least three classes of antimicrobial drugs and were therefore designated as multi-drug resistant. All the selected five virulence genes were detected in the isolates with 39 (69.6%) of the isolates having at least one virulence gene. The virulence genes, ompT and iutA were the most frequent with 33 (58.9%) and 32 (57.1%) isolates respectively; while iroN least occurred in 23 (41.1%) isolates. Of the 56 E. coli isolates, 25 (44.6%) belonged to phylogroup A, 8 (14.3%) belonged to phylogroup B1, 1 (1.8%) belonged to phylogroup B2 and 22 (39.3%) belonged to phylogroup D. None of the 56 APEC isolates generated amplicons of sizes expected for the O1, O2 and O78 serogroups. Out of the seven isolated phages; two had the broadest host range with a combined lytic activity against 14 (25%) of the APEC isolates, coupled with stability to heat up to 60℃ and viability in pH ranging from 2 to 12. These results demonstrate that determining the presence of virulence genes can aid in confirmation of avian colibacillosis. The high level of resistance to the most commonly used antibiotics calls for a search for alternative treatment options like phage therapy in addition to antimicrobial susceptibility testing before treatment so as to limit economic losses due to ineffective treatment.