, 1996). Subsequent studies revealed that the O1 serogroup, which replaced the O139, was a new clone of the O1 El Tor biotype (Faruque et al., 1997; Sharma et al., 1997; Yamasaki et al., 1997). Due to the quiescent period in the incidence of V. cholerae O139, it was thought that the appearance of O139 was a one-time event. But a resurgence of O139 was recorded in August 1996 in Kolkata (Mitra et al., 1996) and this serogroup remained dominant until 1997 (Fig. 1). Between December 1999 and December 2000, escalating association of V. cholerae
O139 with outbreaks of cholera were recorded in many parts of India, including Kolkata Selleckchem ICG-001 (Sinha et al., 2002). After this period, V. cholerae O1 continued to be a dominant serogroup in Kolkata, and the incidence of O139 gradually decreased over the years (Raychoudhuri
et al., 2007) (Fig. 1). Cholera toxin (CT) is the principal toxin of epidemic-causing V. cholerae serogroup O1 and O139 and is encoded by ctxA and ctxB, the major enzymatic subunit and the binding subunit, respectively. Generally, ctxB is polymorphic in nature and exists APO866 solubility dmso in three major genotypes, namely genotype 1, found among strains of the classical biotype worldwide and the US Gulf Coast, genotype 2, found among El Tor biotype strains from Australia and genotype 3, found in El Tor biotype strains from the seventh pandemic and the Latin American epidemic (Olsvik et al., 1993). Previous studies have shown that the V. cholerae serogroup O139 originated from the seventh pandemic El Tor biotype by horizontal transfer of novel O antigen genes (Bik et al., 1995; Comstock et al., 1996).
Cytidine deaminase A recent study revealed that the prototype seventh pandemic El Tor biotype of V. cholerae O1 was completely replaced in 1995 by El Tor strains that had classical type ctxB in Kolkata (Raychoudhuri et al., 2009). This shift of CT from genotype 3 to genotype 1 in V. cholerae O1 strains of Kolkata and detection of diversity in the CTX phage repressor, rstR (Kimsey et al., 1998; Davis et al., 1999; Nusrin et al., 2004), has formed the impetus for a retrospective analysis of CT genotypes along with rstR of CTX prophages in O139 strains isolated from Kolkata over a period of 13 years. A total of 125 O139 strains were selected for this study from the strain repository of the National Institute of Cholera and Enteric Diseases, Kolkata, and were isolated in different time frames between 1993 and 2005. All the strains were grown in Luria–Bertani (LB) broth (Difco) for 18 h and then streaked on Luria agar plates. These strains were confirmed serologically by slide agglutination with O139-specific antiserum. A 1-mL aliquot of overnight LB broth culture was taken into a sterile 1.