[Isolation and characterization of Serratia marcescens phage]

To isolate the bacteriophage of Serratia marcescens (8039) from sewage, and to study on its biological characteristics.

We used Serratia marcescens (8039) as the host to isolate phage from raw sewage from the Sewage Treatment Center of Hospital. Phage SM701 was examined in electron microscope. The genome of SM701 was extracted and the size of its nucleic acid was identified with restriction enzyme analysis. Phage isolated was subjected to plaque forming unit (PFU) assay using double layer agar medium plate method and morphological properties of plaque was observed, and finally optimal MOI multiplicity of infection and one-step growth experiments were carried out.

Phage SM701 specific to Serratia marcescens (8039) was isolated successfully from the raw sewage. SM701 had an isometric polyhedral head (about 64 nm in diameter) and a long noncontractile tail (about 143 nm long). The nucleic acid could be cut off by dsDNA restriction enzyme BamH I or HindIII and its complete size was about 57kb. The plaque of SM701 was transparent about 1mm in diameter at the 12th hour. When MOI equaled 10, the number of phage offspring was higher. One-stepgrowth kinetics was determined according to the results of one-step growth experiment, which showed that the latent period was about 30 min, the rise period was about 100 min, and the average bust size was about 63 pfu/cell.

Phage SM701 belonged to tailed family: siphoviridae and lytic bacteriophage. It was quite easy to observe and count the plaques due to existing color differences between lytic and nonlytic zone.