Chicken-derived coliphage vB_EcoM-E33: isolation, identification, genomic characterization, and evaluation of its therapeutic effect on colibacillosis

Abstract:

[Background] Drug-resistant Escherichia coli is a major pathogen that causes the death of poultry in large-scale breeding. Virulent phages have broad application prospects in preventing and treating drug-resistant bacterial infections. [Objective] To isolate a phage from the environmental samples of chicken farms, identify the biological characteristics, and evaluate its therapeutic effect on colibacillosis in white feather broilers.[Methods] Phage vB_EcoM-E33 (E33) was isolated via double-layer plate method. Its morphological characteristics were observed under a transmission electron microscope. After cloning of the genome sequence, the genomic features of the phage were analyzed. The host range, multiplicity of infection (MOI), stability, and one-step growth curve of phage E33 were determined by double-layer plate method. The colibacillosis model was established with white feather broilers to test the therapeutic effect of phage E33. [Results] A bacteriophage E33 of the family Straboviridae was isolated from a chicken feces sample, with a host range of 35.4% (34/96). The full-length genome of phage E33 was 170 625 bp, including 271 open reading frames (ORFs), two tRNAs, and no virulence or resistance gene. E.coli E32 was used as the host strain for the proliferation of E33, which showed an incubation period of 10 min and a burst size of 60 PFU/cell. When the MOI was 0.001, phage E33 had the highest titer of 1.93×10⁹ PFU/mL. Phage E33 kept stable below 50 ℃ and within the range of pH 3.0-11.0, while it was sensitive to ultraviolet light. The colibacillosis model of white feather broilers was established by oral administration with 10⁸ CFU/mL E.coli O78, and intramuscular injection of 10⁸ PFU/mL phage E33 demonstrated good therapeutic effect on the model. [Conclusion] Phage E33 has a broad host range, high lysis ability, and good tolerance to physical and chemical factors and does not carry harmful genes. It demonstrates a good development value and is expected to be used as an antibiotic alternative for the prevention and control of colibacillosis in chicken farms.