Vibrio parahaemolyticus carrying binary toxin genes, pirAB, is one of the etiological agents causing acute hepatopancreatic necrosis disease (AHPND) in shrimp. This disease has emerged recently as a major threat to shrimp aquaculture worldwide. During a routine PCR screening of AHPND-causing V. parahaemolyticus strains, an isolate tested PCR positive for pirB (R13) and another isolate tested positive for both the pirA and pirB (R14) genes. To evaluate the pathogenicity of these isolates, specific pathogen-free (SPF) Penaeus vannamei were experimentally challenged. For both R13 and R14 isolates, the final survival rate was 100% at termination of the challenge, whereas the final survival with the AHPND-causing V. parahaemolyticus was 0%. The nucleotide sequence of the plasmid DNA carrying the binary toxin genes revealed that R13 contains a deletion of the entire pirA gene whereas R14 contains the entire coding regions of both pirA and pirB genes. However, R14 possesses an insertion upstream of the pirA gene. In R14, mRNA for both pirA and pirB genes could be detected but no cognate proteins. This shows that the genome of AHPND-causing V. parahaemolyticus is highly plastic and, therefore, detection of the pirA and pirB genes alone by DNA-PCR is insufficient as a diagnostic test for AHPND.

中文翻译：

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携带二进制毒素基因但不会引起急性肝胰腺坏死病的副溶血性弧菌pirABVP（+）突变体

携带二进制毒素基因pir AB的溶血弧菌是引起虾急性肝胰腺坏死病（AHPND）的病原体之一。这种疾病最近已成为对全世界虾类水产养殖的主要威胁。在对引起AHPND的副溶血性弧菌菌株进行常规PCR筛选期间，分离株对pirB（R13）的PCR检测呈阳性，而另一分离株对pir A和pir B（R14）的基因检测均为阳性。要评估这些分离株的致病性，请使用无特定病原体（SPF）的南美白对虾被实验挑战。对于R13和R14分离株，在攻击终止时最终存活率为100％，而引起AHPND的副溶血弧菌的最终存活率为0％。携带二元毒素基因的质粒DNA的核苷酸序列表明，R13含有缺失了整个的PIRA基因而R14包含整个编码两者的区域PIR A和PIR乙基因。然而，R14在pir A基因的上游具有插入。在R14中，可以检测到pir A和pir B基因的mRNA，但没有同源蛋白。这表明引起AHPND的副溶血性弧菌的基因组DNA是高度可塑性的，因此仅通过DNA-PCR检测pir A和pir B基因不足以作为AHPND的诊断测试。