Classical ctxB in Vibrio cholerae O1, Kolkata, India

Viral and immunologic examination of human immunodefi ciency virus type-1 infected , persistently seronegative persons. Rapid disease progression without sero-conversion following primary human im-munodefi ciency virus type 1 infection— evidence for highly susceptible human hosts. J, et al. Human immunodefi ciency virus infection and AIDS in a person with negative serology. humoral and cellular immune response to hepatitis C virus NS5 protein after genetic immunization. Alcoholism and rapid progression to AIDS after seroconversion. To the Editor: Among the 206 serogroups of Vibrio cholerae, O1 and O139 are associated with epidemic cholera. Serogroup O1 is classifi ed into 2 biotypes, classical and El Tor. Conventionally, the 2 biotypes can be differentiated on the basis of a set of phenotypic traits. Comparative ge-nomic analysis has shown variations in different genes between these bio-types (1). Cholera toxin (CT), the major toxin responsible for the disease cholera, has 2 epitypes or immunolog-ic forms, CT1 and CT2 (2). Another classifi cation recognizes 3 genotypes on the basis of the ctxB gene sequence variation (3). In the past few years, a new emerging form of V. cholerae O1, which possesses traits of both classical and El Tor biotypes, has been isolated in Bangladesh (4,5), Mozambique (6), Vietnam, Hong Kong, Japan, and Zambia (7). These strains were variously labeled as Matlab variants, hybrids , or altered El Tor strains. Our study analyzed, in chronological order, strains of V. cholerae O1 that were isolated over 17 years (1989– 2005). We used strains isolated during diarrhea surveillance conducted at the Infectious Diseases Hospital, Kol-kata (Calcutta), to determine precisely when the hybrid strains appeared in this region. A total of 171 strains of V. cholerae O1, which were selected to cover different months of each year, were included in this study, along with 2 reference strains for classical and El Tor biotypes. The V. cholerae strains were confi rmed serologically by slide agglutination using a specifi c polyva-lent antiserum to V. cholerae O1. We focused on the ctxB gene. The strains were examined by mis-match amplifi cation mutation assay (MAMA)–based PCR for detecting the ctxB allele; a common forward primer was used for 2 alleles, FW-Com (5′-ACTATCTTCAGCATATGCACAT-GG-3′); and 2 allele-specifi c primers , Re-cla (5′-CCTGGTACTTCTAC TTGAAACG-3′) and Re-elt (5′-CCTGGTACTTCTACTTGAAA CA-3′), were used for classical and El Tor biotypes, respectively (8). Results of the MAMA-PCR are summarized in the Table. All of the 123 V. chol-erae O1 strains from 1995 through …