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

霍乱弧菌在印度次大陆，特别是恒河流域的水生环境中居群，周期性地引起霍乱流行。在206种霍乱弧菌血清型中，只有O1型和139型引起流行性霍乱，而非O1/非o139型不会引起流行性霍乱，尽管观察到散发的腹泻病例。为了明确该地区霍乱的流行特征，对从环境和临床来源分离的霍乱弧菌进行了分析，并对孟加拉地区两种来源的霍乱弧菌分离株进行了分子流行病学分析。采用聚合酶链式反应（PCR）法检测菌株中ctxA、tcpA和toxR毒力基因的含量。PFGE（脉冲场凝胶电泳）测定临床菌株与环境菌株之间的克隆关系。临床源O1和环境源O139菌株3种毒力基因均呈阳性，非O1/非O139菌株除1株外，ctxA和tcpA均呈阴性，但toxR呈阳性。O1和O139最近分离株的PFGE模式在不同来源的各血清型中相似，尽管与过去分离株的比较显示出一些差异。一个特殊的非o1 /非o139菌株。经典型ctxA和tcpA阳性。这些结果表明，临床菌株与环境菌株之间存在克隆关系，水生环境是产毒霍乱弧菌的宿主。

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.