title: 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). Year-wise 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 % in 2006, 2007, 2008, 2009 and 2010, respectively; interestingly, all isolates tested were sensitive to TE in 2011, as observed in 2008. All V. cholerae isolates tested possessed genetic elements such as SXT, ctxAB, tcpA(ET), rstR(ET) and rtxC; none had IntlI (Integron I). Double mismatch amplification mutation assay (DMAMA)-PCR followed by DNA sequencing and analysis of the ctxB gene revealed a point mutation at position 58 (C→A), which has resulted in an amino acid substitution from histidine (H) to asparagine (N) at position 20 (genotype 7) since 2008. Although the multi-resistant strains having tetracycline resistance showed minor genetic divergence, V. cholerae strains were clonal, as determined by a PFGE (NotI)-based dendrogram. This study shows 2008-2010 to be the time of transition from ctxB genotype 1 to genotype 7 in V. cholerae ET causing endemic cholera in Dhaka, Bangladesh.
authors.affiliation: International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh.
authors.forename: Shah M
authors.initials: SM
authors.lastname: Rashed
authors.affiliation: International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh.
authors.forename: Shahnewaj B
authors.initials: SB
authors.lastname: Mannan
authors.affiliation: International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh.
authors.forename: Fatema-Tuz
authors.initials: FT
authors.lastname: Johura
authors.affiliation: International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh.
authors.forename: M Tarequl
authors.initials: MT
authors.lastname: Islam
authors.affiliation: International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh.
authors.forename: Abdus
authors.initials: A
authors.lastname: Sadique
authors.affiliation: National Institute of Infectious Diseases, Tokyo, Japan.
authors.forename: Haruo
authors.initials: H
authors.lastname: Watanabe
authors.affiliation: Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
authors.forename: R Bradley
authors.initials: RB
authors.lastname: Sack
authors.affiliation: Maryland Pathogen Research Institute, University of Maryland, MD, USA.
authors.forename: Anwar
authors.initials: A
authors.lastname: Huq
authors.affiliation: Center for Bioinformatics and Computational Biology, University of Maryland, MD, USA.|Maryland Pathogen Research Institute, University of Maryland, MD, USA.|Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
authors.forename: Rita R
authors.initials: RR
authors.lastname: Colwell
authors.affiliation: International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Cravioto
authors.affiliation: International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh.
authors.forename: Munirul
authors.initials: M
authors.lastname: Alam
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015373:Bacterial Typing Techniques; D001459:Bangladesh / Q000453:epidemiology; D001483:Base Sequence; D002771:Cholera / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology*; D002939:Ciprofloxacin / Q000494:pharmacology; D004269:DNA, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D019353:Endemic Diseases; D004917:Erythromycin / Q000494:pharmacology; D005664:Furazolidone / Q000494:pharmacology; D014644:Genetic Variation; D005839:Gentamicins / Q000494:pharmacology; D006801:Humans; D008826:Microbial Sensitivity Tests; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013420:Sulfamethoxazole / Q000494:pharmacology; D013752:Tetracycline / Q000494:pharmacology; D014295:Trimethoprim / Q000494:pharmacology; D041241:Vibrio cholerae O1 / Q000145:classification / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D005839:Gentamicins; D002939:Ciprofloxacin; D005664:Furazolidone; D004917:Erythromycin; D014295:Trimethoprim; D001618:beta-Lactamases; D013752:Tetracycline; D013420:Sulfamethoxazole