Boyd E Fidelma, Waldor Matthew K
Department of Microbiology, National University of Ireland, University College Cork, Cork, Ireland1.
Howard Hughes Medical Institute and Division of Geographic Medicine and Infectious Diseases, Tufts-New England Medical Center and Tufts University School of Medicine, 750 Washington Street, Boston, MA 02111, USA2.
Microbiology (Reading). 2002 Jun;148(Pt 6):1655-1666. doi: 10.1099/00221287-148-6-1655.
The toxin-coregulated pilus (TCP) is a critical determinant of the pathogenicity of Vibrio cholerae. This bundle-forming pilus is an essential intestinal colonization factor and also serves as a receptor for CTXphi, the filamentous phage that encodes cholera toxin (CT). TCP is a polymer of repeating subunits of the major pilin protein TcpA and tcpA is found within the Vibrio pathogenicity island (VPI). In this study genetic variation at the tcpA locus in toxigenic isolates of V. cholerae was investigated and three novel TcpA sequences from V. cholerae strains V46, V52 and V54, belonging to serogroups O141, O37 and O8, respectively, were identified. These novel tcpA alleles grouped into three distinct clonal lineages. The polymorphisms in TcpA were predominantly located in the carboxyl region of TcpA in surface-exposed regions of TCP fibres. Comparison of the genetic diversity among V. cholerae isolates at the tcpA locus with that of aldA, another locus within the VPI, and mdh, a chromosomal locus, revealed that tcpA sequences are far more diverse than these other loci. Most likely, this diversity is a reflection of diversifying selection in adaptation to the host immune response or to CTXphi susceptibility. An assessment of the functional properties of the variant tcpA sequences in the non-O1 V. cholerae strains was carried out by analysing whether these strains could be infected by CTXphi and colonize the suckling mouse. Similar to El Tor strains of V. cholerae O1, in vitro CTXphi infection of these strains required the exogenous expression of toxT, suggesting that in these strains ToxT regulates TCP expression and that these TcpA variants can serve as CTXphi receptors. All the V. cholerae non-O1 serogroup isolates tested were capable of colonizing the suckling mouse small intestine, suggesting that the different TcpA variants could function as colonization factors.
毒素协同调节菌毛（TCP）是霍乱弧菌致病性的关键决定因素。这种成束菌毛是肠道定植的必需因子，也是CTXphi（编码霍乱毒素（CT）的丝状噬菌体）的受体。TCP是主要菌毛蛋白TcpA重复亚基的聚合物，而tcpA位于霍乱弧菌致病岛（VPI）内。在本研究中，对产毒霍乱弧菌分离株tcpA位点的基因变异进行了研究，鉴定出分别属于O141、O37和O8血清群的霍乱弧菌菌株V46、V52和V54的三个新的TcpA序列。这些新的tcpA等位基因分为三个不同的克隆谱系。TcpA中的多态性主要位于TCP纤维表面暴露区域的TcpA羧基区域。将霍乱弧菌分离株在tcpA位点的遗传多样性与VPI内的另一个位点aldA以及染色体位点mdh的遗传多样性进行比较，发现tcpA序列比其他位点的多样性要高得多。很可能，这种多样性反映了在适应宿主免疫反应或CTXphi易感性方面的多样化选择。通过分析非O1霍乱弧菌菌株是否能被CTXphi感染并定殖于乳鼠体内，对这些菌株中变异tcpA序列的功能特性进行了评估。与霍乱弧菌O1的埃尔托生物型菌株相似，这些菌株的体外CTXphi感染需要外源性表达toxT，这表明在这些菌株中ToxT调节TCP表达，并且这些TcpA变体可以作为CTXphi受体。所有测试的非O1血清群霍乱弧菌分离株都能够定殖于乳鼠小肠，这表明不同的TcpA变体可以作为定植因子发挥作用。
