Protective effects of bacteriophage on experimental Lactococcus garvieae infection in yellowtail

The present study describes the in vitro and in vivo survival of Lactococcu s garvieae bacteriophages and the potential of the phage for controlling ex perimental L. garvieae infection in yellowtail. Anti-L. garvieae phages per sisted well in various physicochemical (water temperature, salinity, pH) an d biological (feed, serum and alimentary tract extracts of yellowtail) cond itions, except for low acidity. In the in vivo, the phage PLgY-16 was detec ted in the spleens of yellowtail until 24 h after intraperitoneal (i.p.) in jection, or the phage was recovered from the intestine of yellowtail 3 h af ter the oral administration of phage-impregnated feed but undetectable 10 h later. Simultaneous administration of live L. garvieae and phage enhanced recovery of the phage from the spleen or intestine. The survival rate was m uch higher in yellowtail that received i.p. injection of the phage after i. p. challenge with L. garvieae, compared with that of control fish without p hage injection. When fish were i.p. injected with phage at different hours after L. garvieae challenge, higher protective effects were demonstrated in fish that received phage treatment at the earlier time. Protection was als o obtained in yellowtail receiving phage-impregnated feed, in which fish we re challenged by an anal intubation with L. garvieae. Anal-intubated L. gar vieae were detected constantly in the spleens of the control fish, while th ey were detected sporadically and disappeared from the phage-treated fish 4 8 h later. On the other hand, orally administered phage was detected at hig h plaque-forming units from the intestines and spleens of the phage-treated fish until 48 h later. These results indicate that intraperitoneally or or ally administered anti-L. garvieae phage prevented fish from experimental L . garvieae infection, suggesting potential use of the phage for controlling the disease.