BIOTYPE-SPECIFIC TCPA GENES IN VIBRIO-CHOLERAE

The tcpA gene, encoding the structural subunit of the toxin-coregulate d pilus, has been isolated from a variety of clinical isolates of Vibr io cholerae, and the nucleotide sequence determined. Strict biotype-sp ecific conservation within both the coding and putative regulatory reg ions was observed, with important differences between the El Tor and c lassical biotypes. V. cholerae O139 Bengal strains appear to have El T or-type tcpA genes. Environmental O1 and non-O1 isolates have sequence s that bind an El Tor-specific tcpA DNA probe and that are weakly and variably amplified by tcpA-specific polymerase chain reaction primers, under conditions of reduced stringency. The data presented allow the selection of primer pairs to help distinguish between clinical and env ironmental isolates, and to distinguish El Tor (and Bengal) biotypes f rom classical biotypes of V. cholerae. While the role of TcpA in chole ra vaccine preparations remains unclear, the data strongly suggest tha t TcpA-containing vaccines directed at O1 strains need include only th e two forms of TcpA, and that such vaccines directed at (O139) Bengal strains should include the TcpA of El Tor biotype.