Effect of Bacteriophages on Vibrio alginolyticus Infection in the Sea Cucumber,Apostichopus japonicus (Selenka)

Vibrio alginolyticus is an important pathogen that causes a variety of diseases in marine animals including the sea cucumber, Apostichopus japonicus. Herein, we describe a two‐phage mixture which may have potential for use as an antibacterial agent to prevent V. alginolyticus infection in the sea cucumber. A Z1210 bacterial isolate was cultured from diseased sea cucumber suffering from skin ulcerations and viscera ejection. The isolate was identified as V. alginolyticus by morphology and sequence similarity analysis. Subsequently, two bacteriophages infecting isolate Z1210 were isolated from the drainpipe of an aquatic market. Morphologically, these two phages were classified as members of Podoviridae (PVA1) and Myoviridae (PVA2) and each phage showed high virulence in an in vitro experiment. Additionally, an experiment conducted in a marine environment showed that a mixture of the two phages increased the survival of sea cucumbers (10 ± 2 g) to 73, 50, and 47% when it was used with a multiplicity of infection of 10, 1, or 0.1, respectively. This result differed markedly from the control without phage (3% survival) while there was no significant difference between the 80 and 47% survival observed for two antibiotic treatments (5 mg/L doxycycline and 10 mg/L kanamycin, respectively).