Abstract: 【Objective】 The phage capable of lysing drug-resistant Serratia marcescens was isolated and the biological characteristics and whole genome analysis of the phage were performed,providing candidate phage for the clinical application of phage therapy to prevent and control Serratia marcescens infection，and offering new ideas for addressing the increasingly problem of drug resistance of Serratia marcescens. 【Method】 In this study,Serratia marcescens Sm2 isolated from sputum samples in hospital was used as the host bacteria,the phage was isolated from sewage sample collected from the sewage treatment system by the plaque method and the double-layer plate method.The biological characteristics of the phage,including morphology,host spectrum,one-step growth curve,temperature tolerance and acid-base stability were further analyzed.Additionally,the whole genome sequence of the phage was determined by the Illumina HisSeq sequencing platform,and the characteristics of the genome and genetic evolution were analyzed. 【Result】 A Serratia marcescens phage vB_SamS_CC02 was isolated from sewage sample collected from the sewage treatment system.This phage formed clear plaques on the LB plate. The observation of transmission electron microscopy indicated that this phage belonged to the Siphoviridae family，was composed of a icosahedral symmetric head with a diameter of (58±10) nm and a tail of length (110±10) nm in length.The host spectrum showed that this phage could only specifically lyse Serratia marcescens and had no lysis effect on other species.One-step growth curve showed that this phage had a 5 min latent period,a lysis cycle of approximately 30 min,and a burst size of up to 105 PFU/cell.The tolerance test results showed that some active phages could still be detected after being stored at 60 ℃ for 60 min,indicating good temperature stability.When placed in a pH 2.0 environment for 60 min,the titer of the phage remained stable at 10⁴ PFU/mL,demonstrating excellent acid-base tolerance.The bioinformatics analysis results showed that the genome of phage vB_SamS_CC02 was 163 764 bp in length,with a GC content of 46%.The genome contained 65 open reading frames (ORFs),without virulence,drug resistance or lysogeny-related genes.Genetic evolutionary analysis results showed that the phage had the highest sequence similarity (96.83%) with Serratia phage vB_SmaS_Serratianator (MW021755.1) at the whole genome level.However,it belonged to a separate evolutionary branch and had a distant relationship with the reported phages based on the evolutionary analysis of the large subunit of the terminase sequence. 【Conclusion】 In this study,a phage vB_SamS_CC02，which could specifically lyse Serratia marcescens was successfully isolated.This phage had strong lytic ability and good stability.This results provided candidate phage for the clinical application of phage therapy in prevention and control drug-resistant Serratia marcescens infection.

Key words: Serratia marcescens; phage; biological characteristics; whole genome analysis