Characterization and Genomic Analysis of a Novel Jumbo Bacteriophage vB_StaM_SA1 Infecting Staphylococcus aureus With Two Lysins

The development of new antimicrobial agents is critically needed due to the alarming increase in antibiotic resistance in bacterial pathogens. Phages have been widely considered as effective alternatives to antibiotics. A novel phage vB_StaM_SA1 (hereinafter as SA1) that can infect multiple Staphylococcus strains was isolated from untreated sewage of a pig farm, which belonged to Myoviridae family. At MOI of 0.1, the latent period of phage SA1 was 55 min, and the final titer reached about 10(9) PFU/mL. The genome of phage SA1 was 260,727 bp, indicating that it can be classified as a jumbo phage. The genome of SA1 had 258 ORFs and a serine tRNA, while only 53 ORFs were annotated with functions. Phage SA1 contained a group of core genes that was characterized by multiple RNA polymerase subunits and also found in phiKZ-related jumbo phages. The phylogenetic tree showed that phage SA1 was a phiKZ-related phage and was closer to jumbo phages compared with Staphylococcus phages with small genome. Three proteins (lys4, lys210, and lys211) were predicted to be associated with lysins, and two proteins with lytic function were verified by recombinant expression and bacterial survival test. Both lys210 and lys211 possessed efficient bactericidal ability, and lys210 could lyse all test strains. The results show that phage SA1 and lys210/lys211 could be potentially used as antibiotic agents to treat Staphylococcus infection.