Rapid spread of the new clone of Vibrio cholerae O1 biotype El Tor in cholera endemic areas in India

SUMMARY Using molecular techniques, we investigated whether the clone of Vibrio cholerae Ol biotype El Tor which appeared in Calcutta, India, in 1994 has spread to other cholera endemic areas in the country. The ribotype of 31 of the 33 strains isolated from different parts of India during 1996 and 1997 was identical to the ribotype displayed by the new clone of V. cholerae Ol which emerged in Calcutta in 1994. Likewise, 12 ofthe 15 strains examined by pulsed-field gel electrophoresis (PFGE) showed identical profile to that exhibited by the new clone of Ol. The restriction fragment length polymorphism (RFLP) of CTX genetic element of these strains also matched with the new clone of Ol which emerged after the outbreak of V. cholerae 0139 in Calcutta. However, two strains (AH042 and AH046) isolated from an outbreak in Ahmedabad (western India) showed different CTX RFLP but had the same ribotype and PFGE profile as the new clone, whereas one strain from Goa (G2) showed distinct ribotype and PFGE profile and the CTX RFLP was identical to the Ol strains which prevailed before the genesis of 0139 in Calcutta. The drug resistance pattern of most of the Ol strains examined in this study, except strain G2, was similar to that of the new clone of V. cholerae Ol. None of the strains in this study carried plasmids. Molecular studies clearly show that the new expanded drug resistant clone of V. cholerae Ol has spread to all cholera endemic areas in India and also provide evidence for the evolution of new clones of the Ol serogroup.