Isolation, Identification And Preliminary Application Of Lytic Phages To Swine Escherichia Coli And Salmonella

E.coli and Salmonella choleraesuis are gram-negative pathogens that widely present in the breeding environment. In recent years, a great number of drug-resistant and multidrug-resistant strains appear constantly with the overuse of antibiotics casuing great economic loss in breeding industry. The prevention and treatment of the diseases caused by E.coli and Salmonella choleraesuis have become increasingly difficult. Phage can specifically infect and kill bacteria due to its natural antiseptic ability. Used as a new substitute for antibiotics, phage receives wide attention.In this study, the drug-resistant E.coli and Salmonella choleraesuis strains were used as the hosts which were screened out by antimicrobial susceptibility test, and isolated the lytic bacteriophage EP-SY and SP3383 from the healthy pig’s feces by double agar method. Meanwhile, the biological characteristics and anti infection preliminary application of phage EP-SY and SP3383 were studied.The results showed that both phage EP-SY and SP3383 had the narrow host spectrum, and their genome was double stranded DNA. They were not sensitive to chloroform and ether, because they had no envelope. Phage EP-SY was found to belong to Myoviridae in Caudovirales with the electron microscopic observations,had an isometrically hexagonal head about 80.00±5.71 nm in diameter and a85.71±9.89 nm tail. It was relatively stable at 40 °C~65 °C or pH 3~12 of the environment. Its optimal MOI was 0.01, the incubation period was 10 min, the burst period was 70 min and the average burst size was about 22.8 PFU per cell. SP3383 belonged to Siphoviridae. The spherical head of the phage was about 41.40±0.33 nm in diameter and the non retractable tail about 96.49±0.38 nm in length. SP3383 had excellent tolerance to temperature, acidic or alkaline environment with the suitable temperature range of 40~65 ℃ and pH range of 4~11. The multiplicity of infection of phage SP3383 was 0.1 and the lantent period was 30 min, the burst phase time was 60 min, and the burst size was 48 PFU per cell. Phage EP-SY and SP3383 had very strong cleavage activities in vitro and had no obvious toxic and side effects on mice.Gavage inoculation with phages could significantly decrease the number of living bacteria in the spleen and intestine of host bacteria infected mice, and the intestinalpathological changes were reduced.In summary, the isolated phage EP-SY and SP3383 could lyse multidrug-resistant strains of E.coli and Salmonella, and played a role in the prevention and treatment of drug resistant bacteria infection in mice. This research lays the foundation for the application of phage instead of antibiotics to control bacterial diseases.