RESUMO
The goal of this study was to isolate and characterize a more complete set of phages that are active against Escherichia coli serogroups O1, O2, and O78, the main causative agents of avian colibacillosis. A mixture of E. coli (O1:K1), (O2:K1), and (O78:K80) was used as a host to isolate phages from wastewater and fecal samples from poultry processing plants. Seven phages were isolated; only 2 of them, EC-Nid1 and EC-Nid2, were selected for further characterization. It was found that EC-Nid1 and EC-Nid2 had icosahedral heads, necks, and contractile tails with tail fibers and therefore belonged to Myoviridae. The phages had genome sizes of 67.06 to 68.04 kb and they lysed all tested strains of E. coli serotype O1, O2, and O78. The 2 phages were resistant to pH 5 to 9, and phage EC-Nid2 was slightly more resistant to acid and alkali environments. Two major protein bands were indicated in EC-Nid (A and D); band D at 45 kDa was a major coat protein and band A was identified as a homolog of endo-N-acetylneuraminidase. It was concluded that phage EC-Nid1 and EC-Nid2 are highly active against O1, O2, and O78 colibacillosis strains.