IFREMER, Station d'Aquaculture de Saint-Vincent, Noumea Cedex, New Caledonia.
J Appl Microbiol. 2010 Jun;108(6):2003-11. doi: 10.1111/j.1365-2672.2009.04601.x. Epub 2009 Oct 28.
A description of bacterial pathogens in shrimp ponds is necessary to understand their pathogenesis. Vibrio nigripulchritudo was shown to contain saprophytic and pathogenic strains among New Caledonian isolates. We established a method to map the development of V. nigripulchritudo in pond sediments at three different genetic levels: the species level, then at the pathogenic cluster level and finally at the plasmid level, present only in all highly pathogenic isolates.
PCR methods were applied to shrimp pond sediments both before and after a mortality outbreak. Using crude samples, the species V. nigripulchritudo is not detected at first (0/42 samples at day 56 post stocking) but appears frequently in the sediments after the mortality event (30/42 at day 107). The distribution of strains from the pathogenic cluster of V. nigripulchritudo also follows this pattern. In contrast, the pSFn1 virulence-associated plasmid was detected in one sample at day 56 and none at day 107. An enrichment method was developed to lower the detection limits of our assays. After enrichment, the species V. nigripulchritudo was detected in all samples at both dates. The number of samples positive for pSFn1 was 42/42 samples at day 56 and 29/42 at day 107.
These results show that the sediments contain V. nigripulchritudo, notably pathogenic strains. Surprisingly, the virulence-associated plasmid pSFn1 found in all V. nigripulchritudo isolated from moribund shrimp appears less frequently in sediments, possibly being useless or even detrimental to its recipient bacteria in this environment.
This study confirms the presence of pathogenic V. nigripulchritudo strains in shrimp pond sediment before a mortality outbreak complying with a previous hypothesis that sediments could be the infecting reservoir. After the outbreak, both total V. nigripulchritudo and pathogenic strains populations have largely increased, possibly contributing to the recurrent mortality observed in this shrimp vibriosis.
描述虾池中细菌病原体对于理解其发病机制十分必要。新喀里多尼亚分离株中的维氏气单胞菌显示出存在腐生性和致病性菌株。我们建立了一种方法来绘制三种不同遗传水平（种水平、致病性簇水平和仅存在于所有高致病性分离株中的质粒水平）下维氏气单胞菌在池塘沉积物中的发展情况。
在死亡率爆发前后，使用 PCR 方法对虾池沉积物进行了检测。使用粗提样品，在最初（投苗后第 56 天，0/42 个样本）未检测到种维氏气单胞菌，但在死亡事件后，沉积物中经常出现（投苗后第 107 天，30/42 个样本）。维氏气单胞菌致病性簇菌株的分布也遵循这种模式。相比之下，pSFn1 毒力相关质粒在第 56 天的一个样本中被检测到，而在第 107 天的样本中则没有。开发了一种富集方法来降低我们检测方法的检测限。富集后，在两个日期的所有样本中均检测到种维氏气单胞菌。pSFn1 阳性样本的数量在第 56 天为 42/42 个样本，在第 107 天为 29/42 个样本。
这些结果表明沉积物中含有维氏气单胞菌，特别是致病性菌株。令人惊讶的是，在濒死虾中分离出的所有维氏气单胞菌中发现的与毒力相关的质粒 pSFn1 在沉积物中出现的频率较低，其在这种环境中对其受体细菌可能是无用的，甚至是有害的。
本研究证实了致病性维氏气单胞菌在死亡率爆发前存在于虾池沉积物中，这与先前的假设一致，即沉积物可能是感染源。爆发后，维氏气单胞菌和致病性菌株的种群数量都大大增加，这可能是导致这种虾类弧菌病反复发生的原因。
