Emergence of Vibrio cholerae O1 biotype El Tor serotype Inaba from the prevailing O1 Ogawa serotype strains in India

Abstract

The toxigenic Inaba serotype of Vibrio cholerae O1 biotype El Tor reappeared in India in 1998 and 1999, almost 10 years after its last dominance in Calcutta in 1989. Extensive molecular characterization by ribotyping, restriction fragment length polymorphism, and pulsed-field gel electrophoresis indicated that recent Inaba strains are remarkably different from the earlier Inaba strains but are very similar to the prevailing V. cholerae O1 Ogawa El Tor biotype strains. The antibiograms of the Inaba strains were also similar to those of the recent V. cholerae Ogawa strains. These V. cholerae O1 Inaba strains appear to have evolved from the currently prevailing Ogawa strains and are likely to dominate in the coming years.

FIG. 1

Ribotypes of representative V. cholerae strains. Lanes: 1, SG24 (O139); 2, 569B (O1, classical Inaba); 3, CO840 (O1, El Tor Ogawa); 4, V2 (O1, Inaba); 5, V13 (O1, Inaba); 6, DO182 (O1, Inaba); 7, DO183 (O1, Inaba); 8, SO86 (O1, Inaba); 9, SO90 (O1, Inaba); 10, SO88 (O1, Ogawa). The positions of λ HindIII molecular size markers are indicated on the left.

FIG. 2

Schematic representations of the organization of the CTX prophage (not to scale) as deduced by Southern hybridization data for V. cholerae O1 Inaba strains represented by V2 (a) and V. cholerae O1 Inaba strains represented by SO85 (b). Arrows and boxes represent the RS elements and the core region of the CTX prophage, respectively, with the hatched portion of the box representing the ctxAB gene. Restriction site abbreviations: BI, BglI; BII, BglII; P, PstI; H, HindIII.

FIG. 3

PFGE profiles of V. cholerae O1 El Tor biotype strains. Lanes: 1, V2 (Inaba); 2, V13 (Inaba); 3, DO182 (Inaba); 4, DO183 (Inaba); 5, SO85 (Inaba); 6, SO88 (Ogawa); 7, SO90 (Inaba); 8, CO840 (Ogawa); 9, PG11 (Ogawa); 10, PG81 (Ogawa); 11, PG117 (Ogawa); 12, PG299 (Ogawa). The positions of bacteriophage λ ladder molecular size markers are indicated on the left.