The Effect of Polyamines on Vibrio cholerae Virulence Properties

Vibrio cholerae is the causative agent of the severe enteric disease, cholera. To be a virulent strain, the bacterium must be able to synthesize both cholera toxin and toxin-coregulated pilus (TCP). TCP has been shown to mediate microcolony formation, which is believed to aid in the colonization and concentration of V. cholerae within the small intestine. Only a few environmental signals have been shown to regulate V. cholerae virulence gene expression. Polyamines have been implicated in regulating virulence gene expression in other bacteria, yet have not been studied in V. cholerae for their effect on virulence properties. Performing agglutination assays we found that all polyamines tested had a negative effect on autoagglutination in a concentration dependent manner. Putrescine and cadaverine significantly affected the synthesis of the major pilin subunit, TcpA; and interestingly, only putrescine had an effect on the relative abundance of the TCP found on the cell surface. The polyamines did not affect pili bundling; however, they inhibited CTX? transduction by 80%, indicating their ability to affect functionality of TCP. From this data we hypothesize the inhibitory autoagglutination effect is caused by the positively charged amine groups on the polyamines electrostatically disrupting the pili-pili interactions which mediate microcolony formation.