A Lytic Bacteriophage with Potential for Inactivation of a Fish Pathogenic Streptococcus agalactiae

摘要

Bacteriophage S14 specific to Streptococcus agalactiae PSOl, a fish pathogenic strain, was isolated from fish pond water. It was a lytic bacteriophage that could lyse all four strains of S. agalactiae used in this study. It was tolerant to high temperature (up to 70°C), to a wide range of pH (3-11), and to antimicrobial chemicals commonly used in aquaculture. One-step growth curve showed that the bacteriophage had latent and burst periods of 40 and 160, respectively and burst size of 145 PFU/infected cell. Transmission electron microscopy reveals that the bacteriophage had an icosahedral head of 52 ± 4.6 nm in diameter and a noncontractile tail of 12 ± 0.4 nm in width and 210 ± 11.8 nm in length. Its nucleic acid was double stranded DNA becauseit was digested by EcoRl, but not by RnaA and nuclease S_1. Based on its morphology and genome, the bacteriophage S14 was likely to be a member of the family Siphoviridae. This study showed that bacteriophage S14 had specificity, host range and stabilityfavoring its use as a therapeutic agent against S. agalactiae infection in aquaculture.