Nebulized Escherichia coli phage YX22 alleviates avian colibacillosis caused by APEC strain IMT5155

Avian colibacillosis caused by avian pathogenic Escherichia coli (APEC) results in high mortality and substantial economic losses in poultry production. Phage therapy represents a promising alternative strategy for controlling bacterial infections. In this study, we isolated the high-titer lytic APEC phage YX22 from poultry farm sewage, and evaluated its therapeutic potential in an experimental APEC infection model. Phage YX22 showed a short latent period of 10 min, a burst size of 158 PFU/cell, and stability across pH 4-10 and 30-60°C for 1 h. Transmission electron microscopy and whole-genome analysis indicated that YX22 belonged to the family Ackermannviridae and the AG3-like virus group. An experimental infection model was established in chicks using APEC strain IMT5155 to compare the effects of nebulized and oral phage administration. YX22 treatment reduced clinical symptom scores, tissue bacterial loads, and lung lesions in infected chicks. The survival rate of chicks receiving nebulized YX22 was 80%, compared with 70% in the oral phage and gentamicin groups and 53.33% in the APEC-challenged control group. Phage recovery assays showed that nebulized YX22 was detected in the respiratory tract within 3 h and in all tested tissues within 10 h. At 10 h after administration, YX22 titers in the lungs and spleen were higher after nebulized administration than after oral administration. These findings suggest that nebulized YX22 has therapeutic potential against experimental avian colibacillosis caused by APEC strain IMT5155, but further studies under production conditions are required.