Takemura Taichiro, Murase Kazunori, Maruyama Fumito, Tran Thi Luong, Ota Atsushi, Nakagawa Ichiro, Nguyen Dong Tu, Ngo Tu Cuong, Nguyen Thi Hang, Tokizawa Asako, Morita Masatomo, Ohnishi Makoto, Nguyen Binh Minh, Yamashiro Tetsu
Vietnam Research Station, Institute of Tropical Medicine, Nagasaki University, Japan.
Section of Microbiology, Graduated School of Medicine, Kyoto University, Japan.
Infect Genet Evol. 2017 Oct;54:146-151. doi: 10.1016/j.meegid.2017.06.017. Epub 2017 Jun 20.
Cholera epidemics have been recorded periodically in Vietnam during the seventh cholera pandemic. Since cholera is a water-borne disease, systematic monitoring of environmental waters for Vibrio cholerae presence is important for predicting and preventing cholera epidemics. We conducted monitoring, isolation, and genetic characterization of V. cholerae strains in Nam Dinh province of Northern Vietnam from Jul 2013 to Feb 2015. In this study, four V. cholerae O1 strains were detected and isolated from 110 analyzed water samples (3.6%); however, none of them carried the cholera toxin gene, ctxA, in their genomes. Whole genome sequencing and phylogenetic analysis revealed that the four O1 isolates were separated into two independent clusters, and one of them diverged from a common ancestor with pandemic strains. The analysis of pathogenicity islands (CTX prophage, VPI-I, VPI-II, VSP-I, and VSP-II) indicated that one strain (VNND_2014Jun_6SS) harbored an unknown prophage-like sequence with high homology to vibriophage KSF-1 phi and VCY phi, identified from Bangladesh and the USA, respectively, while the other three strains carried tcpA gene with a distinct sequence demonstrating a separate clonal lineage. These results suggest that the aquatic environment can harbor highly divergent V. cholera strains and serve as a reservoir for multiple V. cholerae virulence-associated genes which may be exchanged via mobile genetic elements. Therefore, continuous monitoring and genetic characterization of V. cholerae strains in the environment should contribute to the early detection of the sources of infection and prevention of cholera outbreaks as well as to understanding the natural ecology and evolution of V. cholerae.
在第七次霍乱大流行期间，越南曾定期记录到霍乱疫情。由于霍乱是一种水传播疾病，系统监测环境水体中霍乱弧菌的存在对于预测和预防霍乱疫情至关重要。2013年7月至2015年2月，我们在越南北部的南定省对霍乱弧菌菌株进行了监测、分离和基因特征分析。在本研究中，从110份分析水样中检测并分离出4株霍乱弧菌O1菌株（3.6%）；然而，它们的基因组中均未携带霍乱毒素基因ctxA。全基因组测序和系统发育分析表明，这4株O1分离株被分为两个独立的簇，其中一株与大流行菌株的共同祖先发生了分化。对致病岛（CTX噬菌体、VPI-I、VPI-II、VSP-I和VSP-II）的分析表明，一株菌株（VNND_2014Jun_6SS）携带一个未知的前噬菌体样序列，与分别从孟加拉国和美国鉴定出的噬菌体KSF-1 phi和VCY phi具有高度同源性，而其他三株菌株携带tcpA基因，其序列独特，表明为一个独立的克隆谱系。这些结果表明，水生环境可能含有高度分化的霍乱弧菌菌株，并作为多种与霍乱弧菌毒力相关基因的储存库，这些基因可能通过移动遗传元件进行交换。因此，持续监测环境中的霍乱弧菌菌株并进行基因特征分析，应有助于早期发现感染源和预防霍乱暴发，以及了解霍乱弧菌的自然生态和进化。
