Prophage phiv142-3 enhances the colonization and resistance to environmental stresses of avian pathogenic Escherichia coli.

Bacterial acquisition of prophages reflects natural selection. Phage DNA has been shown to constitute up to 20% if bacterial genomes. However, prophages' role in Avian Pathogenic Escherichia coli (APEC) is unclear. In this study, APEC strain DE142 harboring prophage phiv142-3, was subjected to deletion and the WT and deletion mutant were characterized under a range of conditions. Prophage deletion mutant DE142Δphiv142-3 was constructed and characterized. The DE142Δphiv142-3 colonies were much smaller than those of the wild-type, and the mutant cells were elongated. The mutant showed reduced adherence to DF-1 cells (87.4% reduction) compared to the wild-type (P < 0.001), and showed a significantly decreased resistance to the killing action of serum (P < 0.001). The mutant demonstrated 95.6%, 71.6%, and 99.6% reduced survival under acid, alkaline, and oxidative stress, respectively. In vitro competition assays showed that the cell number of the mutant was about one-tenth that of the wild-type (competitive index (CI) value, 0.1177). In vivo, the mutant showed significantly decreased colonization of chicken tissues compared with the wild-type. Thus phiv142-3 helps DE142 cope with adverse environments and aids bacterial colonization.