Study On Application Of Bacteriophage In Treating Rabbit Colibacillosis

Pathogenic Escherichia coli(E.coli)is severely threatening the rabbit industry in China,and the concern about antibiotic-resistant bacteria has made an urgent need for antibiotic alternatives.Two experiments were carried out to evaluate the efficacy of phage therapy on systematic or intestinal E.coli infection.In exp.1,a member(ZRP1)of Myoviridae family was isolated from rabbit feces by using a strain of rabbit atypical enteropathogenic E.coli(ZR1)as host.The one-step growth curve indicated that the latent period was about 25 to 30 min and the burst size was 144 PFU/cell.The rate of phage-resistant mutation was 7 × 10-5.When the bacteriophage input at the multiplicity of infection(MOI)of 0.1,1 or 10,the growth of host E.coli in broth was inhibited for 5 hr.A single intravenous injection of ZRP1 at MOI 0.1,1 or 10 significantly prolonged the survival time of rabbits simultaneously received lethal dose of ZR1.In exp.2,45 rabbits were equally divided into three groups after they were orally inoculated with pathogenic E.coli to induce gut infection.Each group was treated with bacteriophage ZRP1(Group P),ciprofloxacin lactate(Group A),or phosphate-buffered solution(PBS)(Group N).Another 15 healthy rabbits composed the control group(Group C).The body weight gain decreased significantly,but the white blood cell count,especially the percentage of large white blood cells,and the serum endotoxin levels increased significantly after infection.The result of microscopic examination of the ileum showed that E.coli ZR1 adhered to villi and caused hemorrhage inside the villi.Group P and Group A rabbits recovered after treatments,and both bacteriophage and antibiotic treatment significantly decreased the E.coli eaeA gene concentration in cecal contents.The microbiota in cecal contents changed in infected rabbits only treated with PBS.The relative abundance of Clostridiales and YS2 decreased significantly but the relative abundance of Enterobacteriales increased significantly.According to the principal components analysis,the microbiota of Group P and Group C rabbits were similar to one another in type and relative abundance but different from those of Group N and Group A rabbits.The results demonstrated that oral administration of bacteriophage can cure gut infection with minimal impact on the cecal microbiota.In conclusion,phage therapy,as antibiotic alternative,is therapeutically viable to treat rabbit colibacillosis.