Examination of Diverse Toxin-Coregulated Pilus-Positive Vibrio cholerae Strains Fails To Demonstrate Evidence for Vibrio Pathogenicity Island Phage

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American Society for Microbiology

RESUMO

The major virulence factors of toxigenic Vibrio cholerae are cholera toxin, which is encoded by a lysogenic filamentous bacteriophage (CTXΦ), and toxin-coregulated pilus (TCP), an essential colonization factor that is also the receptor for CTXΦ. The genes involved in the biosynthesis of TCP reside in a pathogenicity island, which has been reported to correspond to the genome of another filamentous phage (designated VPIΦ) and to encode functions necessary for the production of infectious VPIΦ particles. We examined 46 V. cholerae strains having diverse origins and carrying different genetic variants of the TCP island for the production of the VPIΦ and CTXΦ in different culture conditions, including induction of prophages with mitomycin C and UV irradiation. Although 9 of 10 V. cholerae O139 strains and 12 of 15 toxigenic El Tor strains tested produced extracellular CTXΦ, none of the 46 TCP-positive strains produced detectable VPIΦ in repeated assays, which detected as few as 10 particles of a control CTX phage per ml. These results contradict the previous report regarding VPIΦ-mediated horizontal transfer of the TCP genes and suggest that the TCP island is unable to support the production of phage particles. Further studies are necessary to understand the mechanism of horizontal transfer of the TCP island.

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