Effect of bdellovibrios to the contamination of Vibrio parahaemolyticus to marine fishes and shellfishes.

在进行流行病学调查以确定引起副溶血性弧菌肠胃炎爆发的食物时，其中一个困难的问题是，在很多个案中，未能从怀疑引起副溶血性弧菌肠胃炎爆发的海产品中检测出副溶血性弧菌的耐热直接溶血素菌株。在流行病学调查前，笔者推测沿海地区（包括渔港和渔场）的海产品中存在蛭弧菌和产TDH菌株，而产TDH菌株已被蛭弧菌感染致死。在冲绳县冲绳县元渊町渡口港的海水中检测到125株能裂解副溶血性弧菌菌株的蛭弧菌。分离的114株蛭弧菌对15株产TDH的副溶血性弧菌的裂解谱可分为56种类型。蛭弧菌Cd 22菌株对副溶血弧菌D3菌株的裂解活性在盐度为35-10‰的人工海水中稳定，但在盐度为5‰以下的海水中不稳定，表明该蛭弧菌属海洋细菌，不能裂解河口不稳定的副溶血弧菌。支持蛭弧菌菌株Yd 9 -1生长的菌株D3的浓度为10^8 cfu/ml或更高。用菌株D3和Yd 9 -1污染斑节对虾（Penaeus monodon），并在5℃下保存，与不含Yd 9 -1的样品相比，菌株D3在4 d内下降至10%以下。这些证据表明，副溶血性弧菌污染的海产品在冰箱储存期间会被蛭弧菌感染而死亡。

One of the difficult problems in the epidemiological survey to identify the causative food of an outbreak of Vibrio parahaemolyticus-gastroenteritis is that thermostable direct hemolysin (TDH) -producing strains of V.parahaemolyticus could not be detected from marine products suspected to be causative foods in many cases. I supposed that seafood would be contaminated with bdellovibrios as well as TDH-producing strains at the coastal areas including fishing ports and fishing farms and that TDH-producing strains had been killed by the infection of bdellovibrios before the epidemiological survey.We detected 125 strains of Bdellovibrio to lyse V.parahaemolyticus strains from the seawater at Toguchi Port in Motobu-cho, Okinawa Prefecture. Lytic spectra of the isolated 114 Bdellovibrio strains to 15 TDH producing V.parahaemolyticus strains were categorized to 56 types. Lytic activity of Bdellovibrio strain Cd22 to V.parahaemolyticus strain D3 was stable in artificial seawater with a salinity of 35-10‰ but not stable in the seawater with a salinity of 5‰ or less, suggesting that the bdellovibrio strain would be marine bacterium and that it could not lyse V.parahaemolyticus unstable at estuaries. Concentrations of strain D3 to support the growth of Bdellovibrio strain Yd9-1 was 10^8 cfu/ml or more. When shrimp (Penaeus monodon) was contaminated with strains D3 and Yd9-1 and kept in 5℃, strain D3 decreased to 10% or less within 4 days compared with samples without Yd9-1. These evidences suggest that V.parahaemolyticus strains contaminated to the seafood would be killed by the infection of bdellovibrios at the storage in the refrigerator.