TCPA PILIN SEQUENCES AND COLONIZATION REQUIREMENTS FOR O1 AND O139 VIBRIO-CHOLERAE

The distribution, characterization and Function of the tcpA gene was i nvestigated in Vibrio cholerae O1 strains of the El Tor biotype and in a newly emergent non-O1 strain classified as serogroup O139. The V. c holerae tcpA gene from the classical biotype strain O395 was used as a probe to identify a clone carrying the tcpA gene from the El Tor biot ype strain E7946. The sequence of the E7946 tcpA gene revealed that th e mature El Tor TcpA pilin has the same number of residues as, and is 82% identical to, TcpA of classical biotype strain O395. The majority of differences in primary structure are either conservative or cluster ed in a manner such that compensatory changes retain regional amino ac id size, polarity and charge. In a functional analysis, the cloned gen e was used to construct an El Tor mutant strain containing an insertio n in fcpA. this strain exhibited a colonization defect in the infant m ouse cholera model similar in magnitude to that previously described f or classical biotype tcpA mutants, thus establishing an equivalent rol e for TCP in intestinal colonization by El Tor biotype strains. The tc pA analysis was further extended to both a prototype El Tor strain fro m the Peru epidemic and to the first non-Ol strain known to cause epid emic cholera, an O139 V. cholerae isolate from the current widespread Asian epidemic. These strains were shown to carry tcpA with a sequence identical to E7946. these results provide further evidence that the n ewly emergent non-O1 serogroup O139 strain represents a derivative of an El Tar biotype strain and, despite its different LPS structure, sha res common TCP-associated antigens. Therefore, there appear to be only two related sequences associated with TCP pilin required for coloniza tion by all strains responsible for epidemic cholera, one primary sequ ence associated with classical strains and one for El Tor strains and the recent O139 derivative. A diagnostic correlation between the prese nce of tcpA and the ability of V. cholerae to colonize and cause clini cal cholera is now extended to strains of both O1 and non-O1 serotypes .