Ecological and molecular-epidemiological studies of Vibrio cholerae related bacteria in Indian Subcontinent

霍乱弧菌在印度次大陆，特别是恒河盆地的水环境中定居，并周期性地引起霍乱流行。在206个霍乱弧菌血清中，只有O1和139引起霍乱流行，而非O1/非O139菌株不会引起霍乱，尽管观察到零星的腹泻病例。为明确霍乱在该地区的流行特征，从环境来源和临床来源分离霍乱弧菌并进行分析，重点分析孟加拉地区两种来源霍乱弧菌的分子流行病学特征。用聚合酶链式反应(PCR)方法分析毒力基因(ctxA、tcpA和toxR)在分离株中的存在。采用脉冲场凝胶电泳法(PFGE)分析临床菌株与环境菌株之间的克隆关系。临床来源和环境来源的O1和O139菌株均为3种毒力基因阳性，而非O1/非O139菌株除1株外，ctxA和tcpA均为阴性，毒素R均为阳性。新近分离的O1和O139分离株的PFGE图谱在每个血清型上相似，无论来源如何，尽管与过去的分离株相比显示出一些差异。一种特殊的非O1/非O139菌株。CtxA、tcpA呈典型阳性。这些结果表明，霍乱弧菌临床菌株与环境菌株之间存在克隆关系，水环境是产毒霍乱弧菌的蓄水池。

Vibrio cholerae colonizes aquatic environments in Indian-subcontinent, especially in Ganges Basin, and causes cholera epidemics periodically. Of the 206 serovars of V.cholerae, only O1 and 139 cause epidemic cholera, whereas non-O1/non-O139 strains do not, although sporadic diarrheal cases are observed. To clarify epidemic feature of cholera in these area, V.cholerae strains were isolated from from environmental and clinical origins and analysed.V.cholerae isolates from both origins in the Bengal region were analyzed with particular emphasis on the molecular epidemiological feature. Presence of the virulence genes (ctxA,tcpA and toxR) in the isolates was analyzed by PCR(polymerase chain reaction) method. PFGE (pulsed-field gel electrophoresis) was performed to determine the clonal relationships between clinical and environmental strains. O1 and O139 strains from both clinical and environmental sources were all positive for the three virulence genes while nonO1/non-O139 strains from both sources were all negative for ctxA and tcpA, except a strain, but positive for toxR. PFGE patterns of recent isolates of O1 and O139 were similar in each serovar regardless of origins, although comparison with past isolates showed some differences. An exceptional non-O1/non-O139 strain. was positive for ctxA and tcpA of classical type. These results indicate that there is a clonal relationship between clinical and environmental strains and the aquatic environments serve as reservoirs of toxigenic V.cholerae.