Plasmid-mediated sulfamethoxazole resistance encoded by the sul2 gene in the multidrug-resistant Shigella flexneri 2a isolated from patients with acute diarrhea in Dhaka, Bangladesh

PLoS One. 2014 Jan 9;9(1):e85338. doi: 10.1371/journal.pone.0085338. eCollection 2014.

Abstract

In this study, mechanisms of plasmid-mediated sulfamethoxazole resistances in the clinical strains of multi-drug resistant (MDR) Shigella flexneri 2a were elucidated for the first time in Bangladesh. From 2006 to 2011, a total of 200 S. flexneri 2a strains were randomly selected from the stock of the Enteric and Food Microbiology Laboratory of icddr,b. Antimicrobial susceptibility of the strains showed 73%, 98%, 93%, 58%, 98%, 64% and 4% resistance to trimethoprim-sulfamethoxazole, nalidixic acid, ampicillin, erythromycin, tetracycline, ciprofloxacin and ceftriaxone respectively. Plasmid profiling revealed heterogeneous patterns and interestingly, all the trimethoprim-sulfamethoxazole resistant (SXT(R)) strains yielded a distinct 4.3 MDa plasmid compared to that of the trimethoprim-sulfamethoxazole susceptible (SXT(S)) strains. Curing of this 4.3 MDa plasmid resulted in the susceptibility to sulfamethoxazole alone suggesting the involvement of this plasmid in the resistance of sulfamethoxazole. Moreover, PCR analysis showed the presence of sul2 gene in SXT(R) strains which is absent in SXT(S) strains as well as in the 4.3 MDa plasmid-cured derivatives, confirming the involvement of sul2 in the resistance of sulfamethoxazole. Furthermore, pulsed-field gel electrophoresis (PFGE) analysis revealed that both the SXT(R) and SXT(S) strains were clonal. This study will significantly contributes to the knowledge on acquired drug resistance of the mostly prevalent S. flexneri 2a and further warrants continuous monitoring of the prevalence and correlation of this resistance determinants amongst the clinical isolates of Shigella and other enteric pathogens around the world to provide effective clinical management of the disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acute Disease
  • Anti-Bacterial Agents / therapeutic use*
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Bacterial Typing Techniques
  • Bangladesh / epidemiology
  • Carrier Proteins / genetics*
  • Carrier Proteins / metabolism
  • Diarrhea / drug therapy
  • Diarrhea / epidemiology
  • Diarrhea / microbiology
  • Drug Resistance, Multiple, Bacterial / genetics*
  • Dysentery, Bacillary / drug therapy
  • Dysentery, Bacillary / epidemiology
  • Dysentery, Bacillary / microbiology
  • Electrophoresis, Gel, Pulsed-Field
  • Gene Expression
  • Humans
  • Plasmids*
  • Shigella flexneri / drug effects*
  • Shigella flexneri / genetics
  • Shigella flexneri / isolation & purification
  • Sulfamethoxazole / therapeutic use*
  • Trimethoprim, Sulfamethoxazole Drug Combination / therapeutic use

Substances

  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Carrier Proteins
  • Sul2 protein, bacteria
  • Trimethoprim, Sulfamethoxazole Drug Combination
  • Sulfamethoxazole

Grants and funding

This study was funded by icddr,b (www.icddrb.org) and its donors which provide unrestricted support to icddr,b for its operations and research. Current donors providing unrestricted support include: Government of the People's Republic of Bangladesh; Canadian International Development Agency (CIDA), Embassy of the Kingdom of the Netherlands (EKN), Swedish International Development Cooperation Agency (Sida), and the Department for International Development, UK (DFID). The authors gratefully acknowledge these donors for their support and commitment to icddr,b research efforts. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.