The toxin-coregulated pilus is a colonization factor and protective antigen of Vibrio choleraeEl Tor

Abstract

We have previously shown that insertional inactivation of tcpA, the gene encoding the major pilin subunit of the toxin-coregulated pilus (TCP), renders Vibrio choleraeO1 strains of El Tor biotype virtually avirulent in the infant mouse cholera model (IMCM). We now report that more refined mutants, bearing an in-frame deletion in tcpA, show a similar dramatic attenuation in vivo. In mixed-infection competition experiments the ratio of wild-type:mutant vibrios increased c. 10 3–10 5fold during a period of in vivogrowth. An attempt to complement the Δ tcpAmutants by providing a functional El Tor tcpAgene in transwas 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 isolates of the novel O139 serovar. These sera failed to protect against challenge with a strain of classical biotype, nor could antibodies to classical TCP confer immunity to El Tor challenge. We conclude that TCP is a critical colonization factor of V. choleraeO1 El Tor and that antibodies to TCP are sufficient to confer protection against such strains in the IMCM. Our data suggest that the biotype-specific epitopes carried by TcpA are of greater vaccine significance than those epitopes common to both proteins.