HETEROGENEITY IN THE ORGANIZATION OF THE CTX GENETIC ELEMENT IN STRAINS OF VIBRIO-CHOLERAE O139 BENGAL ISOLATED FROM CALCUTTA, INDIA AND DHAKA, BANGLADESH AND ITS POSSIBLE LINK TO THE DISSIMILAR INCIDENCE OF O139 CHOLERA IN THE 2 LOCALES

After a lapse of 33 months, Vibrio cholerae O139. the new serogroup as sociated with cholera, has re-emerged in Calcutta, India and has becom e the dominant serogroup causing cholera from September 1996. In neigh bouring Bangladesh, V. cholerae O1 biotype El Tor continues to be the dominant cause of cholera with the O139 serogroup accounting for only a small proportion of cases. Comparison of the phenotypic traits of re presentative O139 strains from Calcutta and Dhaka isolated between Dec ember 1996 and April 1997 showed similar phenotypic traits with the ex ception that Dhaka O139 strains were susceptible to streptomycin whils t Calcutta O139 strains were resistant. The Dhaka and Calcutta O139 st rains displayed identical ribotypes but showed remarkable differences in the structure and organization of the CTX genetic element. In the D haka O139 strains, two copies of the CTX element were arranged in tand em and this resembled the pattern displayed by the 1992 epidemic strai ns of O139. The Calcutta O139 strains, in contrast, carried three copi es of the CTX genetic element arranged in tandem with the loss of a co nserved Bg/II restriction site in the RS1 element and the appearance o f a new HindIII site in the same region. While there may be other fact ors, it appears that the reorganization of the CTX genetic element in the Calcutta O139 strains may have contributed to the resurgence of th is serogroup in Calcutta. (C) 1998 Academic Press Limited.