International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh.
National Institute of Infectious Diseases, Tokyo, Japan.
J Med Microbiol. 2012 Dec;61(Pt 12):1736-1745. doi: 10.1099/jmm.0.049635-0. Epub 2012 Sep 13.
Vibrio cholerae O1 biotype El Tor (ET), causing the seventh cholera pandemic, was recently replaced in Bangladesh by an altered ET possessing ctxB of the Classical (CL) biotype, which caused the first six cholera pandemics. In the present study, V. cholerae O1 strains associated with endemic cholera in Dhaka between 2006 and 2011 were analysed for major phenotypic and genetic characteristics. Of 54 representative V. cholerae isolates tested, all were phenotypically ET and showed uniform resistance to trimethoprim/sulfamethoxazole (SXT) and furazolidone (FR). Resistance to tetracycline (TE) and erythromycin (E) showed temporal fluctuation, varying from year to year, while all isolates were susceptible to gentamicin (CN) and ciprofloxacin (CIP). Year-wise data revealed erythromycin resistance to be 33.3 % in 2006 and 11 % in 2011, while tetracycline resistance accounted for 33, 78, 0, 100 and 27 % in 2006, 2007, 2008, 2009 and 2010, respectively; interestingly, all isolates tested were sensitive to TE in 2011, as observed in 2008. All V. cholerae isolates tested possessed genetic elements such as SXT, ctxAB, tcpA(ET), rstR(ET) and rtxC; none had IntlI (Integron I). Double mismatch amplification mutation assay (DMAMA)-PCR followed by DNA sequencing and analysis of the ctxB gene revealed a point mutation at position 58 (C→A), which has resulted in an amino acid substitution from histidine (H) to asparagine (N) at position 20 (genotype 7) since 2008. Although the multi-resistant strains having tetracycline resistance showed minor genetic divergence, V. cholerae strains were clonal, as determined by a PFGE (NotI)-based dendrogram. This study shows 2008-2010 to be the time of transition from ctxB genotype 1 to genotype 7 in V. cholerae ET causing endemic cholera in Dhaka, Bangladesh.
霍乱弧菌 O1 生物型 El Tor（ET）引起了第七次霍乱大流行，最近在孟加拉国被具有古典生物型 ctxB 的改变的 ET 取代，古典生物型引起了前六次霍乱大流行。在本研究中，分析了 2006 年至 2011 年期间在达卡地方性霍乱中相关的霍乱弧菌 O1 菌株的主要表型和遗传特征。在测试的 54 个代表性霍乱弧菌分离株中，所有均表现为 ET 表型，并且对甲氧苄啶/磺胺甲噁唑（SXT）和呋喃唑酮（FR）具有均匀的耐药性。四环素（TE）和红霉素（E）的耐药性呈逐年波动，每年都有所不同，而所有分离株均对庆大霉素（CN）和环丙沙星（CIP）敏感。逐年数据显示，2006 年红霉素耐药率为 33.3％，2011 年为 11％，而四环素耐药率分别为 2006 年、2007 年、2008 年、2009 年和 2010 年的 33％、78％、0％、100％和 27％；有趣的是，2011 年所有测试的分离株均对 TE 敏感，这与 2008 年的观察结果一致。所有测试的霍乱弧菌分离株均具有 SXT、ctxAB、tcpA（ET）、rstR（ET）和 rtxC 等遗传元件；均没有 IntlI（整合子 I）。双重错配扩增突变分析（DMAMA）-PCR 随后进行 DNA 测序和 ctxB 基因分析显示，在位置 58 处发生点突变（C→A），导致从 2008 年开始第 20 位氨基酸由组氨酸（H）突变为天冬酰胺（N）（基因型 7）。尽管具有四环素耐药性的多耐药菌株表现出较小的遗传差异，但霍乱弧菌菌株是克隆的，如 NotI 脉冲场凝胶电泳（PFGE）-基于的系统发育树所示。本研究表明，2008 年至 2010 年是导致孟加拉国达卡地方性霍乱的 ET 霍乱弧菌 ctxB 基因型从 1 型向 7 型转变的时期。
