Application of the bacteriophage pVco-14 to prevent Vibrio coralliilyticus infection in Pacific oyster (Crassostrea gigas) larvae

Vibrio coralliilyticus infects a variety of shellfish larvae, including Pacific oyster (Crassostrea gigas) larvae worldwide, and remains a major constraint in marine bivalve aquaculture practice, especially in artificial seed production facilities. In this study, we isolated and characterized the bacteriophage (phage) that specifically infects V. coralliilyticus. The phage was designated pVco-14 and classified as Siphoviridae. We also investigated the potential efficacy of the isolated phage against V. coralliilyticus infection. We conducted a survey to replace the overuse of antibiotics, which generate multi-antibiotic-resistant strains and causes environmental pollution. The latent period of pVco-14 was estimated to be approximately 30 min, whereas the burst size was 13.3 PFU/cell. The phage was found to infect four strains of tested V. coralliilyticus. pVco-14 was stable at wide temperature (4-37 degrees C) and pH (5.0-9.0) ranges. Eighty-one percent of oyster larvae died in an immersion challenge at a dose 1.32 x 10(5) CFU/ml of virulent V. coralliilyticus (strain 58) within 24 h. When oyster larvae were pre-treated with the phage before the bacterial challenge (bacterial conc.: 1.32 x 10(4) and 1.32 x 10(5) CFU/ml), mortality of the phage-treated oyster larvae was lower than that of the untreated control. These results suggest that pVco-14 has potential to be used as a prophylactic agent for preventing V. coralliilyticus infection in marine bivalve hatcheries and can reduce the overuse of antibiotics.