Therapeutic Effects of Antimicrobial Compounds against Bacillary Necrosis of Larval Pacific Oyster

Abstract

Eight antimicrobial compounds were examined to evaluate their therapeutic effects against experimentally or naturally induced vibriosis of the Pacific oysterCrassostrea gigas. In experimental infections with a strain ofVibrio splendidusbiovar II, a causative agent of bacillary necrosis of cultured triploid oyster larvae, chloramphenicol (CP) exhibited complete protection against challenges at 10⁵or 10⁶CFU/mL, and erythromycin (EM), novobiocin (NB), gentamicin and streptomycin (SM) were effective to reduce the mortality, but nalidixic acid or oxytetracycline was not. CP and EM were also highly effective against experimental infections with other six strains ofVibriospecies (V. splendidusbiovar ll, V. pelagiusI, V. campbellii, and V. tubiashii) which had been isolated from oyster larvae or the rearing water, but NB and SM were less effective. On the other hand, not only CP and EM but also NB and SM exhibited higher protection against the natural infection.