Faruque S M, Saha M N, Alim A R, Albert M J, Islam K M, Mekalanos J J
Molecular Genetics Laboratory, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka-1000, Bangladesh.
Infect Immun. 1998 Dec;66(12):5819-25. doi: 10.1128/IAI.66.12.5819-5825.1998.
Toxigenic Vibrio cholerae strains are lysogens of CTXPhi, a filamentous phage which encodes cholera toxin. The receptor for CTXPhi for invading V. cholerae cells is the toxin-coregulated pilus (TCP), the genes for which reside in a larger genetic element, the TCP pathogenicity island. We analyzed 146 CTX-negative strains of V. cholerae O1 or non-O1 isolated from patients or surface waters in five different countries for the presence of the TCP pathogenicity island, the regulatory gene toxR, and the CTXPhi attachment sequence attRS, as well as for susceptibility of the strains to CTXPhi, to investigate the molecular basis for the emergence of new clones of toxigenic V. cholerae. DNA probe or PCR assays for tcpA, tcpI, acfB, toxR, and attRS revealed that 6.85% of the strains, all of which belonged to the O1 serogroup, carried the TCP pathogenicity island, toxR, and multiple copies of attRS, whereas the remaining 93.15% of the strains were negative for TCP but positive for either one or both or neither of toxR and attRS. An analysis of the strains for susceptibility to CTXPhi, using a genetically marked derivative of the phage CTX-KmPhi, showed that all TCP-positive CTX-negative strains and 1 of 136 TCP-negative strains were infected by the phage either in vitro or in the intestines of infant mice. The phage genome integrated into the chromosome of infected V. cholerae O1 cells forming stable lysogens. Comparative analysis of rRNA gene restriction patterns revealed that the lysogens derived from nontoxigenic progenitors were either closely related to or distinctly different from previously described clones of toxigenic V. cholerae. To our knowledge, this is the first demonstration of lysogenic conversion of naturally occurring nontoxigenic V. cholerae strains by CTXPhi. The results of this study further indicated that strains belonging to the O1 serogroup of V. cholerae are more likely to possess the TCP pathogenicity island and hence to be infected by CTXPhi, leading to the origination of potential new epidemic clones.
产毒性霍乱弧菌菌株是CTXΦ的溶原菌，CTXΦ是一种丝状噬菌体，可编码霍乱毒素。CTXΦ侵入霍乱弧菌细胞的受体是毒素共调节菌毛（TCP），其基因位于一个更大的遗传元件——TCP致病岛上。我们分析了从五个不同国家的患者或地表水中分离出的146株霍乱弧菌O1或非O1的CTX阴性菌株，检测其是否存在TCP致病岛、调节基因toxR和CTXΦ附着序列attRS，以及这些菌株对CTXΦ的敏感性，以研究产毒性霍乱弧菌新克隆出现的分子基础。针对tcpA、tcpI、acfB、toxR和attRS的DNA探针或PCR检测显示，6.85%的菌株（均属于O1血清群）携带TCP致病岛、toxR和多个attRS拷贝，而其余93.15%的菌株TCP呈阴性，但toxR和attRS其中之一、两者或均为阴性。使用噬菌体CTX-KmΦ的基因标记衍生物对菌株进行CTXΦ敏感性分析表明，所有TCP阳性的CTX阴性菌株以及136株TCP阴性菌株中的1株，在体外或幼鼠肠道中均被该噬菌体感染。噬菌体基因组整合到被感染的霍乱弧菌O1细胞的染色体中，形成稳定的溶原菌。rRNA基因限制性图谱的比较分析表明，源自无毒祖先的溶原菌与先前描述的产毒性霍乱弧菌克隆密切相关或明显不同。据我们所知，这是首次证明CTXΦ对自然存在的无毒霍乱弧菌菌株进行溶原性转化。本研究结果进一步表明，霍乱弧菌O1血清群的菌株更有可能拥有TCP致病岛，因此更容易被CTXΦ感染，从而导致潜在新流行克隆的产生。
