coli DH5[alpha] was performed and existence of ctxB
in vector was confirmed by restriction enzyme analysis (Figure 1B).
Conventional biotyping methods and a combination of MAMA-and conventional- PCRs were used for classifying the strains into prototype El Tor, hybrid, or El Tor variant biotypes, based on their ctxB
and rstR genes (21-23).
We studied the genotype of ctxB
using a double-mismatch amplification mutation PCR (i.
in Vibrio cholerae O1, Kolkata, India.
One of the reasons could be higher CT production by El Tor variant strains possessing classical ctxB
gene allele than typical El Tor (35).
Another classification identifies three types of ctxB
genes based on three non random base changes resulting in modifications in the deduced amino acid sequence.
cholerae ET has shown genetic changes since 2001, and isolates carry the ctxB
gene of the CL biotype ([ctxB
0 (Applied Maths, Kortrijk, Belgium); ctxB
genotyping was also performed as described (10).
cholerae across the country, each of the 170 isolates was biotype El Tor and carried the classical ctxB
allele, as measured by mismatch amplification mutation PCR.
Since the early 1990s, the El Tor variant strains, which are biotypes of El Tor but carry the classical type of ctxB
, have emerged and prevail in multiple regions where cholera is endemic (1,3-6).
Chromosome I of Haiti isolate 2010EL-1786 harbors 1 hybrid CTX[PHI] characterized by a 1-nt variant of the classical ctxB
-7) and El Tor rstR flanked by a toxinlinked cryptic element and El Tor-type RS1 element with an intact rstC locus (Figure 3).
The sequencing results for ctxB
and tcpA and PCR results for rstR and the VC2346 gene are shown in Table 5.