Isolation,Identification And Genomic Analysis Of Escherichia Coli Phage SZH-1

Antibiotics are the main means to prevent and control bacteria,but the selection pressure of antibiotics leads to the death of sensitive strains,and drug-resistant strains are screened out and gradually become the dominant strains.The research and development speed of new antibiotics cannot prevent the prevalence of drug-resistant strains,resulting in treatment failures of drug-resistant bacterial infection.Mankind is facing a risk to go back to "pre antibiotic era".Lytic phage is a bacterial virus that can cleave and kill specific host bacteria.It is a microorganism endowed by nature to balance bacteria.At present,it has become one of the important choices to replace antibiotics against bacterial infection.E.coli is a kind of normal microorganism that generally exists in human and animals,but it can cause human diseases under some conditions.Among the bacterial infections that need to find antibiotic substitutes published by the World Health Organization,Enterobacteriaceae ranks in the forefront.In this study,we tried to isolate the bacteriophage against Escherichia coli from hospital sewage.A lytic bacteriophage was purified by double-layer agar method and named as SZH-1.Based on the morphology under transmission electron microscope,SZH-1 can be classified as a member of Caudovirales and Siphoviridae with a total length of 160 nm,a head with 56 nm in diameter and a noncontractible tail at length of103 nm.The optimal multiplication of infection(MOI)of phage SZH-1 was 0.001.Under,optimal MOI,one step growth curve of SZH-1 showed that the incubation period was 10 min and the outbreak time was 40 min.Among total of 29 tested strains,11 strains of E.coli are sensitive host of SZH-1.SZH-1 showed high activity at p H 8,and will be completely inactivated at range of p H 1-2 or 13-14.The genome of phage SZH-1 is double circular DNA at length of 44096 bp and the content of GC is 51%.The genome of SZH-1 contains 81 open reading frames(ORFs).Among them,26 ORFs locate in positive chain and resting 55 ORFs locate in negative chain.The products of 32 ORFs have been annotated and the products of other49 ORFs are named as hypthetical proteins.And there is no t RNA was produced by SZH-1 genome.In conclusion,a lytic phage against E.coli named as SZH-1 was purified and identified,and the genome of SZH-1 was also analyzed and submitted into Gen Bank.