Laboratory of Genomic Research on Pathogenic Bacteria, International Research Center for Infectious Diseases, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Infect Immun. 2010 Apr;78(4):1772-80. doi: 10.1128/IAI.01051-09. Epub 2010 Jan 19.
Vibrio parahaemolyticus, one of the human-pathogenic vibrios, causes three major types of clinical illness: gastroenteritis, wound infections, and septicemia. Thermostable direct hemolysin (TDH) secreted by this bacterium has been considered a major virulence factor of gastroenteritis because it has biological activities, including cytotoxic and enterotoxic activities. Previous reports revealed that V. parahaemolyticus strain RIMD2210633, which contains tdh, has two sets of type III secretion system (T3SS) genes on chromosomes 1 and 2 (T3SS1 and T3SS2, respectively) and that T3SS1 is responsible for cytotoxicity and T3SS2 is involved in enterotoxicity, as well as in cytotoxic activity. However, the relative importance and contributions of TDH and the two T3SSs to V. parahaemolyticus pathogenicity are not well understood. In this study, we constructed mutant strains with nonfunctional T3SSs from the V. parahaemolyticus strain containing tdh, and then the pathogenicities of the wild-type and mutant strains were evaluated by assessing their cytotoxic activities against HeLa, Caco-2, and RAW 264 cells, their enterotoxic activities in rabbit ileal loops, and their lethality in a murine infection model. We demonstrated that T3SS1 was involved in cytotoxic activities against all cell lines used in this study, while T3SS2 and TDH had cytotoxic effects on a limited number of cell lines. T3SS2 was the major contributor to V. parahaemolyticus-induced enterotoxicity. Interestingly, we found that both T3SS1 and TDH played a significant role in lethal activity in a murine infection model. Our findings provide new indications that these virulence factors contribute to and orchestrate each distinct aspect of the pathogenicity of V. parahaemolyticus.
副溶血性弧菌是人类致病性弧菌之一，可引起三种主要临床疾病：肠胃炎、伤口感染和败血症。该细菌分泌的耐热直接溶血素（TDH）被认为是肠胃炎的主要毒力因子，因为它具有细胞毒性和肠毒性等生物学活性。先前的报告表明，含有 tdh 的副溶血性弧菌菌株 RIMD2210633 在染色体 1 和 2 上分别有两套 III 型分泌系统（T3SS）基因（分别为 T3SS1 和 T3SS2），并且 T3SS1 负责细胞毒性，T3SS2 参与肠毒性以及细胞毒性。然而，TDH 和两个 T3SS 对副溶血性弧菌致病性的相对重要性和贡献尚不清楚。在这项研究中，我们从含有 tdh 的副溶血性弧菌菌株中构建了 T3SS 无功能突变株，然后通过评估野生型和突变株对 HeLa、Caco-2 和 RAW 264 细胞的细胞毒性、对兔回肠环的肠毒性以及在小鼠感染模型中的致死性来评估它们的致病性。我们证明 T3SS1 参与了本研究中使用的所有细胞系的细胞毒性活性，而 T3SS2 和 TDH 对有限数量的细胞系具有细胞毒性作用。T3SS2 是副溶血性弧菌诱导肠毒性的主要因素。有趣的是，我们发现 T3SS1 和 TDH 在小鼠感染模型中的致死活性中都发挥了重要作用。我们的研究结果提供了新的证据，表明这些毒力因子有助于并协调副溶血性弧菌致病性的各个不同方面。
