Genetic characteristics of drug-resistant Vibrio cholerae O1 causing endemic cholera in Dhaka, 2006–2011

Abstract

Vibrio cholerae O1 biotype El Tor (ET), causing the seventh cholera pandemic, was recently replaced in Bangladesh by an altered ET possessing ctxB of the Classical (CL) biotype, which caused the first six cholera pandemics. In the present study, V. cholerae O1 strains associated with endemic cholera in Dhaka between 2006 and 2011 were analysed for major phenotypic and genetic characteristics. Of 54 representative V. cholerae isolates tested, all were phenotypically ET and showed uniform resistance to trimethoprim/sulfamethoxazole (SXT) and furazolidone (FR). Resistance to tetracycline (TE) and erythromycin (E) showed temporal fluctuation, varying from year to year, while all isolates were susceptible to gentamicin (CN) and ciprofloxacin (CIP). Yearwise data revealed erythromycin resistance to be 33.3 % in 2006 and 11 % in 2011, while tetracycline resistance accounted for 33, 78, 0, 100 and 27 %

CtxB1 outcompetes CtxB7 in Vibrio cholerae O1, Bangladesh

“…The ctxB sequencing data (GenBank accession nos KT278766-KT278777) of the respective genotype, ctxB1 or ctxB7, were found to be consistent with the MAMA and DMAMA-PCR results. The ctxB genotyping data revealed that all V. cholerae O1 strains isolated from cholera cases had ctxB7 in 2010 (100 %; 11/11) and 2011 (100 %; 9/ 9), as reported earlier (Rashed et al, 2012). Although the number of V. cholerae clinical strains included in 2012 was low (n510), the majority of these strains (60 %; 6/10) carried ctxB1, and the ctxB7 was detected from the remaining V. cholerae associated with endemic cholera in Dhaka, Bangladesh.…”

“…cholerae was isolated from the stools of cholera patients admitted at the icddr,b Dhaka Hospital (Dhaka, Bangladesh); and the environmental isolates were from water samples routinely collected every fortnight from the water bodies in and around Dhaka city. A total of 151 conveniently chosen V. cholerae (70 clinical and 81 environmental) isolated between 2010 and 2014 by standard culture methods were subjected to phenotypic and genotypic tests (Alam et al, 2006;Rashed et al, 2012). All isolates were serologically confirmed to be V. cholerae O1, and possessed 'O' serogoup-specific gene wbe O1, further confirming the serological results; and they were positive for cholera toxin gene, ctxA (Hoshino et al, 1998).…”

“…A similar change from ctxB1 to ctxB7 also occurred in V. cholerae O1 responsible for endemic cholera in Dhaka, Bangladesh, but not before 2008 (Rashed et al, 2012), suggesting a possible transmission of V. cholerae carrying the ctxB7 from neighbouring India, which was detected later in Africa and Haiti (Hasan et al, 2012). Here, in the present study, we report yet another temporal change in the ctxB genotype of the V. cholerae population, showing that the ctxB1 returned and re-established dominance in 2013-2014, outcompeting ctxB7, which was dominant in the preceding years in V. cholerae associated with endemic cholera in Dhaka, Bangladesh (Rashed et al, 2012).…”

“…1b). While the basis for the temporal selection of ctxB genotype in V. cholerae responsible for endemic cholera is yet to be understood, V. cholerae O1 isolated from cholera patients carried ctxB7, not ctxB1, during 2010-2011 (Rashed et al, 2012 increased in the environment (93 %; 14/15), and ctxB1 was found associated with cholera after about 2 years of consistent absence. Subsequently, all V. cholerae O1 isolated from the aquatic environment carried ctxB1 in 2013 (100 %; 15/15) and 2014 (100 %; 15/15) (Fig.…”

Phenotypic and genetic characteristics of Vibrio cholerae O1 carrying Haitian ctxB and attributes of classical and El Tor biotypes isolated from Silvassa, India

“…It was noted that altered El Tor strains replaced the prototype of the seventh pandemic El Tor in Asia (Evins et al, 1995;Nair et al, 2002) and Africa (Lizarraga-Partida et al, 2009;Morita et al, 2008). However, the Haitian ctxB variant of V. cholerae was reported to cause epidemics in Asia and Africa (Bhattacharya et al, 2016;Goel et al, 2008;Naha et al, 2012;Rashed et al, 2012;Talkington et al, 2011). Allelic variations in ctxB, tcpA and rstR are used as a marker to differentiate and characterize CTXF types and track the origin of strains.…”