A virulent bacteriophage of Lactococcus garvieae (formerly Enterococcus seriolicida) isolated from yellowtail Seriola quinqueradiata

Abstract

A virulent bacteriophage, designated PLgY, was detected from cultures of Lactococcus garvieae (formerly Enterococcus seriolicida) isolated from diseased yellowtail Seriola quinqueradiata. The phage had an isometric head measuring 50 to 60 nm, a thin flexible tail of 7 x 140-180 nm, and the genome consisting of double stranded DNA, indicating that PLgY is a member of the family Siphoviridae. Of 26 strains of L. garvieae examined, 24 were sensitive to the phage but 2 strains of L. garvieae and another 22 strains of bacteria including fish and shellfish-pathogenic bacteria were not. Lysis of L. garvieae cells due to the phage infection was dependent on culture temperature and occurred at between 17 and 29°C. Although an infection experiment of young yellowtail revealed that the 2 phage-insensitive L. garvieae strains were less virulent than 2 phage-sensitive strains, there was no correlation between phage sensitivity and antigenic variation.