Abstract
BackgroundIncrease in the number of multidrug resistant pathogens and the accompanied rise in case fatality rates has hampered the treatment of many infectious diseases including cholera. Unraveling the mechanisms responsible for multidrug resistance in the clinical isolates of Vibrio cholerae would help in understanding evolution of these pathogenic bacteria and their epidemic potential. This study was carried out to identify genetic factors responsible for multiple drug resistance in clinical isolates of Vibrio cholerae O1, serotype Ogawa, biotype El Tor isolated from the patients admitted to the Infectious Diseases Hospital, Kolkata, India, in 2009.Methodology/Principal FindingsOne hundred and nineteen clinical isolates of V. cholerae were analysed for their antibiotic resistance phenotypes. Antibiogram analysis revealed that majority of the isolates showed resistance to co-trimoxazole, nalidixic acid, polymixin B and streptomycin. In PCR, SXT integrase was detected in 117 isolates and its sequence showed 99% identity notably to ICEVchInd5 from Sevagram, India, ICEVchBan5 from Bangladesh and VC1786ICE sequence from Haiti outbreak among others. Antibiotic resistance traits corresponding to SXT element were transferred from the parent Vibrio isolate to the recipient E. coli XL-1 Blue cells during conjugation. Double-mismatch-amplification mutation assay (DMAMA) revealed the presence of Haitian type ctxB allele of genotype 7 in 55 isolates and the classical ctxB allele of genotype 1 in 59 isolates. Analysis of topoisomerase sequences revealed the presence of mutation Ser83 → Ile in gyrA and Ser85→ Leu in parC. This clearly showed the circulation of SXT-containing V. cholerae as causative agent for cholera in Kolkata.ConclusionsThere was predominance of SXT element in these clinical isolates from Kolkata region which also accounted for their antibiotic resistance phenotype typical of this element. DMAMA PCR showed them to be a mixture of isolates with different ctxB alleles like classical, El Tor and Haitian variants.
Highlights
Vibrio cholerae is a Gram-negative pathogen that causes cholera, an acute dehydrating diarrhoea which is globally important as it occurs in endemic, epidemic and pandemic forms [1,2]
There was predominance of SXT element in these clinical isolates from Kolkata region which accounted for their antibiotic resistance phenotype typical of this element
Double-mismatch-amplification mutation assay (DMAMA) PCR showed them to be a mixture of isolates with different ctxB alleles like classical, El Tor and Haitian variants
Summary
Vibrio cholerae is a Gram-negative pathogen that causes cholera, an acute dehydrating diarrhoea which is globally important as it occurs in endemic, epidemic and pandemic forms [1,2]. The acquisition and dissemination of antibiotic resistance genes is mediated by mobile genetic elements like plasmids, integrons and transposons [3]. One such transposon is SXT element, an integrative conjugative element (ICE) that integrates and replicates with the host chromosome, can excise itself and be transferred between bacteria by conjugation [4]. This study was carried out to identify genetic factors responsible for multiple drug resistance in clinical isolates of Vibrio cholerae O1, serotype Ogawa, biotype El Tor isolated from the patients admitted to the Infectious Diseases Hospital, Kolkata, India, in 2009
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