To prevent the spread of antibiotic resistance, bacteriophages have gradually become the most promising alternative to antibiotics for treating bacterial infectious diseases. In this study, using E. coli DC1 as the host strain, we isolated a bacteriophage named Escherichia coli phage XJA18 from farm sewage. We conducted morphological identification, host range determination, biological characteristic analysis, genomic feature analysis, and evaluation of in vitro and in vivo antibacterial effects. Electron microscopy revealed that phage XJA18 belongs to the class Caudoviricetes, with an icosahedral head and a non-contractile long tail. Whole-genome sequencing revealed that the phage has dsDNA with a length of 50,572 bp, with a GC content of 45.33%. The genome does not contain any antibiotic resistance genes or virulence genes, indicating good safety. XJA18 showed lytic activity against 24% of clinically isolated E. coli strains. The optimal multiplicity of infection (MOI) was 0.001, with a latent period of 10 min, a burst period of 30 min, and a burst size of 2.22 × 102 PFU/cell. It remained stable at 4–50 °C and pH 4–12. In vitro antibacterial results revealed that XJA18 had the most pronounced initial bacterial growth suppression at MOI = 0.001 during the first 4 h. In vivo experiments demonstrated that both prophylactic and therapeutic administration of XJA18 could protect against E. coli infection, significantly reducing inflammatory cytokine levels and bacterial loads in the livers and spleens of mice (p < 0.001), significantly increasing body weight (p < 0.05), and reducing histopathological damage to the colon, liver, and lungs. In summary, phage XJA18 can effectively inhibit E. coli and is safe and stable. These characteristics indicate that phage XJA18 has great potential as a novel biological agent to replace antibiotics for treating bacterial infectious diarrhea in calves.
Qin et al. (Thu,) studied this question.