Bacteriophage activity against and characterisation of avian pathogenicEscherichia coliisolated from colibacillosis cases in Uganda

A laboratory-based study aimed at establishing a stock of avian pathogenic Escherichia coli (APEC) lytic bacteriophages, for future development of cocktail products for controlling colibacillosis as well as minimizing use of antimicrobial drugs in the poultry production systems in Uganda. Specifically, the study determined the antibiotic susceptibility; phylogenetic categories, occurrence of selected virulence genes among Escherichia coli stock isolates from cases of chicken colibacillosis; and isolation of specific bacteriophages. Fifty six isolates were confirmed as E. coli by standard phenotypic tests. All the 56 (100%) 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. Phylogenetically, APEC isolates mainly belonged to phylogroups A and D which represented 44.6% and 39.3%, respectively. 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 isolates, 69.6% harbored at least one virulence gene, while 50% had at least four virulence genes; hence confirmed as APEC. None of the isolates belonged to the selected serotypes O1, O2 and O78. Seven specific bacteriophages were isolated and their host range, varied from 1.8% to 17.9% (n=56 APEC isolates), while the combined lytic spectrum of all the phages was 25%. Phage stability was negatively affected by increasing temperatures with both UPEC04 and UPEC10 phages becoming undetectable at 70°C; however activity was detected between pH 2 and 12. The high occurrence of APEC isolates with resistance against the commonly used antibiotics supports the need for alternative strategies of bacterial infections control in poultry. The low host range exhibited by the phages calls for search for more candidates before more in-depth studies are done for phage characterization and application.