Structure and arrangement of the cholera toxin genes in Vibrio cholerae O139.

The sequence of the ctxB gene encoding the B subunit of cholera toxin has been determined for a strain of Vibrio cholerae of the novel O139 serotype associated with recent outbreaks of severe cholera throughout South-East Asia and found to be identical to the ctxB gene in V. cholerae O1 of the El Tor biotype. Analyses by Southern hybridization and PCR showed that all strains of the O139 serotype V. cholerae tested carried cholera toxin genes and other genes associated with a virulence cassette DNA region at two loci identical or homologous to those identified in the Classical rather than the El Tor biotype of V. cholerae serotype O1 although these loci in O139 could reside on restriction fragments of variable size.