Mass mortality among the post-larvae of cultured abalone Haliotis diversicolor supertexta has occurred on the south coast of China since 2002. The diseased abalone are generally 10 to 30 days old, and typical signs of the disease include them turning white in colour and falling off the diatom films on which they were cultured. Among sixteen different motile bacteria isolated from the diseased post-larvae, four were identified as Vibrio parahaemolyticus on the basis of biochemical characteristics when compared with those of a V. parahaemolyticus type strain ATCC 17802T. Isolate 25, a representative isolate of V. parahaemolyticus recovered from diseased abalone, was virulent for the post-larvae with an LD50 value of 3.5 × 105 CFU (colony forming units)/ml. All moribund post-larvae artificially infected with the bacterium turned white and fell off the diatom films on which they were cultured as seen to occur during natural outbreaks of the disease, and it was possible to recover the bacterium from artificially infected post-larvae. The results of the study indicate that V. parahaemolyticus is a pathogenic bacterium to abalone post-larvae.

噬菌蛭弧菌具有裂解病原菌、净化水体的功效，从海洋环境中分离到4 株Bh04 系列蛭弧菌，对其生长条件进行了测定，同时研究了它们对61 株菌株的裂解能力。结果表明，在1%～3%的盐度范围内，蛭弧菌均可生长，最适盐度为3%！；在15～ 30！温度条件下蛭弧菌也可生长，但最适培养温度为20_25；只有在使用活的宿主菌的培养条件下，蛭弧菌才能生长。4株蛭弧菌分别可裂解21、24、4 0、43 株菌，各占总试验菌数（61）的344%、393%、656%和70 5%。4 株蛭弧菌一起，则可裂解55 菌株，占总试验菌株的902%。研究结果揭示了蛭弧菌在消除海洋环境中有害细菌方面的潜在应用价值。

An epidemic of mass mortality of abalone (Haliotis diversicolor supertexta) postlarvae aged 40 days or less has existed across south coast of China since the second half of 2002. Among 20 bacterial strains isolated from diseased abalone postlarvae on 2216E marine agar plates during an outbreak of postlarval disease in August 2005, a predominant strain (designated strain 20) was demonstrated to be virulent to postlarvae with an LD50 value of 1.0-105 colony forming units (CFU ml 1) on day 4, while the other 19 strains were either avirulent (16 strains) or weakly virulent (3 strains). The same bacterium could be re-isolated from postlarvae after bacterial challenge using 2216E marine agar plates. Preliminary toxicity tests of ECPs of strain 20 revealed that at 2.77 mg protein ml 1, crude ECPs completely liquefied postlarvae within 24 h, leaving only shells. API 20E analysis identified strain 20 as Klebsiella oxytoca. 16S and ITS rDNA sequencing and phylogenetic analyses further confirmed this identification. Antibiotic susceptibility tests showed that strain 20 exhibited 94% of susceptibility to 16 various antibiotics tested and only showed resistance to streptomycin. Results of this work demonstrated that K. oxytoca is also linked to this epidemic in Fujian, China. This is considered to be the first report regarding K. oxytoca involved in the mass mortality of postlarval abalone in south China and the world.

Outbreaks of mass mortality among cultured postlarvae of abalone Haliotis diversicolor supertexta aged between 7 and 30 days occurred since 2002 on the south coast of China. Among 24 bacterial strains isolated from diseased abalone postlarvae on 2216E Marine and TCBS agar plates during an outbreak in July 2003, 23 were avirulent whilst a predominant strain (designated as strain 2) was highly virulent to postlarvae with an LD50 value under 1.0×103 colony forming units (CFU) ml−1. All the moribund/dead postlarvae exhibited the same gross symptoms as that observed in natural outbreaks. The same bacteria could be re-isolated from postlarvae after bacterial challenge using 2216E Marine and TCBS agar plates. API analysis identified it to be Vibrio parahaemolyticus with 99% confidence. 16S and ITS rDNA sequencing analysis also revealed it to be highly homologous with Vibrio parahaemolyticus. Kanagawa reaction and PCR amplification of TDH gene on strain 2 proved to be negative. Antibiotic susceptibility tests showed that strain 2 exhibited 56.25% of susceptibility to chemotherapeutic agents tested, and was resistant to penicillin G, amikacin, trimethoprim–sulfamethoxazole, tetracycline, ciprofloxacin, novobiocin and neomycin. Results in this study reveal that V. parahaemolyticus strain 2 is an infectious agent to abalone postlarvae in South China.