Genetic analysis of the colonization mechanisms of Vibrio cholerae

The Gram-negative bacterium Vibrio cholerae is the causative agent of the diarrheal disease cholera, which is estimated to affect millions of persons worldwide each year. Although the profuse diarrhea characteristic of the disease results from the action of cholera enterotoxin, V. cholerae must first colonize the gastrointestinal tract of the host. Colonization is broadly defined as the process by which V. cholerae establishes an infection and persists in the host, and this process also appears to influence the safety and efficacy of live, attenuated cholera vaccines.;The most important colonization factor identified to date in V. cholerae is the toxin-coregulated pilus (TCP), which consists of polymerized TcpA pilin subunits. Detailed analysis of TcpA mutations constructed analogously to pilin mutations known to affect autoagglutination in N. gonorrhoeae determined that the phenotypes of autoagglutination, colonization, and serum resistance were all associated with TcpA. The finding that autoagglutination is also adversely affected in V. cholerae supports the theory that structural similarities among type IV pilins reflect certain functional similarities.;In further studies, signature-tagged transposon mutagenesis (STM) was employed to perform the first screen of a large random bank of transposon insertion mutants for colonization-defective mutants. This screen identified several genes involved in TCP biogenesis, and purine, biotin, and lipopolysaccharide biosynthetic pathways were also found to be critical for colonization. Other identified loci had no previously known function in pathogenesis, and one had no homology to any known genes. Two STM-identified loci appear to encode phosphotransferases, and since mutations in these genes reduce production of both toxin and TCP, these putative phosphotransferases are apparently involved in control of the ToxR regulon. Contrary to a recent report, evidence of an adverse effect of LPS mutations on TCP production was not found in these studies.