Fluoroquinolone resistance mechanisms of Shigella flexneri isolated in Bangladesh

PLoS One. 2014 Jul 16;9(7):e102533. doi: 10.1371/journal.pone.0102533. eCollection 2014.

Abstract

Objective: To investigate the prevalence and mechanisms of fluoroquinolone resistance in Shigella species isolated in Bangladesh and to compare with similar strains isolated in China.

Methods: A total of 3789 Shigella isolates collected from Clinical Microbiology Laboratory of icddr,b, during 2004-2010 were analyzed for antibiotic susceptibility. Analysis of plasmids, plasmid-mediated quinolone-resistance genes, PFGE, and sequencing of genes of the quinolone-resistance-determining regions (QRDR) were conducted in representative strains isolated in Bangladesh and compared with strains isolated in Zhengding, China. In addition, the role of efflux-pump was studied by using the efflux-pump inhibitor carbonyl cyanide-m-chlorophenylhydrazone (CCCP).

Results: Resistance to ciprofloxacin in Shigella species increased from 0% in 2004 to 44% in 2010 and S. flexneri was the predominant species. Of Shigella spp, ciprofloxacin resistant (CipR) strains were mostly found among S. flexneri (8.3%), followed by S. sonnei (1.5%). Within S. flexneri (n = 2181), 14.5% were resistance to ciprofloxacin of which serotype 2a was predominant (96%). MIC of ciprofloxacin, norfloxacin, and ofloxacin were 6-32 mg/L, 8-32 mg/L, and 8-24 mg/L, respectively in S. flexneri 2a isolates. Sequencing of QRDR genes of resistant isolates showed double mutations in gyrA gene (Ser83Leu, Asp87Asn/Gly) and single mutation in parC gene (Ser80Ile). A difference in amino acid substitution at position 87 was found between strains isolated in Bangladesh (Asp87Asn) and China (Asp87Gly) except for one. A novel mutation at position 211 (His→Tyr) in gyrA gene was detected only in the Bangladeshi strains. Susceptibility to ciprofloxacin was increased by the presence of CCCP indicating the involvement of energy dependent active efflux pumps. A single PFGE type was found in isolates from Bangladesh and China suggesting their genetic relatedness.

Conclusions: Emergence of fluoroquinolone resistance in Shigella undermines a major challenge in current treatment strategies which needs to be followed up by using empirical therapeutic strategies.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bangladesh
  • Base Sequence
  • China
  • DNA Gyrase / genetics
  • DNA Mutational Analysis
  • DNA Primers / genetics
  • DNA Topoisomerase IV / genetics
  • Drug Resistance, Bacterial / genetics
  • Drug Resistance, Bacterial / physiology*
  • Electrophoresis, Gel, Pulsed-Field
  • Fluoroquinolones / pharmacology*
  • Genes, Bacterial / genetics
  • Microbial Sensitivity Tests
  • Molecular Sequence Data
  • Shigella flexneri / drug effects*
  • Species Specificity

Substances

  • DNA Primers
  • Fluoroquinolones
  • DNA Topoisomerase IV
  • DNA Gyrase

Grants and funding

This research study was funded by the icddr,b’s core donors and Government of Bangladesh through IHP-HNPRP. icddr,b acknowledges with gratitude the commitment of Government of Bangladesh through IHP-HNPRP to its research efforts. icddr,b also gratefully acknowledges the following donors which provide unrestricted support: Australian Agency for International Development (AusAID), Government of the People’s Republic of Bangladesh, Canadian International Development Agency (CIDA), Swedish International Development Cooperation Agency (Sida), and the Department for International Development, UK (DFID). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.