Isolation and characterization of a novel lytic phage ФSM9-3Y of Serratia marcescens

Objective To explore the biological characteristics of Serratia marcescens phages isolated from sewage for a further investigation to develop phage agents against drug-resistant Serratia marcescens.Methods Lytic phages of Serratia marcescens were isolated and identified by using a double-agar method,the specificity of phages to host cells was observed.Phage samples for observation by electron microscopy were carried out with negative-stain.The extracted genomes of lytic phages were analyzed with restriction enzymes on electrophoresis,the multiplicity of infection and one-step growth experiment of phages were evaluated.The protein patterns of phages were completed by SDS-PAGE.Results 7 lytic phages of Serratia marcescens were isolated from raw sewage,one of these,ФSM9-3Y,was further studied.Electron microscopy revealed ФSM9-3Y having an icosahedral head(70 nm) and a tail(50 nm in length).The multiplicity of infection(MOI) of ФSM9-3Y was 1,the one-step growth curve of ФSM9-3Y showed that the latent-period is 30 min,burst-period is 70 min,and the burst size is 629 PFU/cell.DNA electrophoresis indicated that the genome is double-stranded DNA estimated to be 54 kb in size.SDS-PAGE demonstrated a total of 13 protein bands with a relative molecular quality ranging from 25 to 130 kD.A major protein band,with a relative molecular quality of 48 kD,was observed.Conclusion The phage ФSM9-3Y was capable of efficient lysis of Serratia marcescens.According to its biological features,the lytic phage,ФSM9-3Y,belongs to Caudovirale order,Myoviridae family.