THE TOXIN-COREGULATED PILUS IS A COLONIZATION FACTOR AND PROTECTIVE ANTIGEN OF VIBRIO-CHOLERAE EL-TOR

We have previously shown that insertional inactivation of tcpA, the ge ne encoding the major pilin subunit of the toxin-coregulated pilus (TC P), renders Vibrio cholerae O1 strains of El Tor biotype virtually avi rulent in the infant mouse cholera model (IMCM). We now report that mo re refined mutants, bearing an in-frame deletion in tcpA, show a simil ar dramatic attenuation in vivo. In mixed-infection competition experi ments the ratio of wildtype:mutant vibrios increased c. 10(3)-10(5) fo ld during a period of in vivo growth. An attempt to complement the Del ta tcpA mutants by providing a functional El Tor tcpA gene in trans wa s only partially successful. Sera raised against El Tor TcpA were able to passively protect infant mice against challenge with TCP-positive strains of homologous biotype and were also protective against isolate s of the novel O139 serovar. These sera failed to protect against chal lenge with a strain of classical biotype, nor could antibodies to clas sical TCP confer immunity to El Tor challenge. We conclude that TCP is a critical colonization factor of V. cholerae O1 El Tor and that anti bodies to TCP are sufficient to confer protection against such strains in the IMCM. Our data suggest that the biotype-specific epitopes carr ied by TcpA are of greater vaccine significance than those epitopes co mmon to both proteins. (C) 1996 Academic Press Limited