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Updated: May 2, 2026
A High-throughput Platform for the Screening of Salmonella spp./Shigella spp.
Published on: November 7, 2018
Molecular characterization and PCR-based replicon typing of multidrug resistant Shigella sonnei isolates from an
Sirigade Ruekit1, Sonam Wangchuk, Tshering Dorji
1Department of Enteric Diseases, Armed Forces Research Institute of Medical Sciences (AFRIMS), Bangkok, Thailand. sirigader@afrims.org.
Background:
Shigella species are an important cause of diarrhea in developing countries. These bacteria normally acquire their antibiotic resistance via several different mobile genetic elements including plasmids, transposons, and integrons involving gene cassettes. During a diarrhea surveillance study in Thimphu, Bhutan in June and July, 2011, Shigella sonnei were isolated more frequently than expected. This study describes the antibiotic resistance of these S. sonnei isolates.
Methods:
A total of 29 S. sonnei isolates from Thimphu, Bhutan was characterized for antimicrobial susceptibility by disc diffusion assay and minimum inhibitory concentration (MIC) assay. All isolates were tested by pulsed-field gel electrophoresis (PFGE) with restriction enzyme XbaI and were tested for plasmid. The plasmid patterns and the PFGE patterns were analyzed by Bionumerics software. DNA sequencing was performed on amplified products for gyraseA gene and class 1 and class 2 integrons. S. sonnei isolates were classified for incompatibility of plasmids by PCR-based replicon typing (PBRT).
Results:
These S. sonnei were resistant to multiple drugs like ciprofloxacin, nalidixic acid, trimethoprim-sulfamethoxazole, streptomycin, and tetracycline but susceptible to azithromycin. All isolates had class 2 integrons dfrA1, sat1 and aadA1 genes. Two point mutations in Gyrase A subunit at position Ser83Leu and Asp87Gly were detected in these quinolone resistant isolates. The plasmid and PFGE patterns of S. sonnei isolates suggested a clonal relationship of the isolates. All isolates carried common ColE plasmid. ColE plasmid co-resided with B/O plasmid (nine isolates) or I1 plasmid (one isolate).
Conclusions:
The characteristics of 29 S. sonnei isolates from Thimphu, Bhutan in June and July, 2011 are identical in PFGE, plasmid and resistance pattern. This study suggests that these recent S. sonnei isolates are clonally related and multidrug-resistant.
Insights
Multidrug-resistant Shigella sonnei strains were identified in Bhutan, showing clonal relationships and resistance to common antibiotics. These findings highlight the need for ongoing surveillance of infectious diseases in the region.
Area of Science:
- Microbiology
- Infectious Diseases
- Genetics
Background:
- Shigella species are a major cause of diarrhea in developing nations.
- Antibiotic resistance in Shigella is often acquired through mobile genetic elements.
- An increased isolation of Shigella sonnei during a surveillance study in Bhutan prompted this investigation.
Purpose of the Study:
- To characterize the antibiotic resistance profiles of Shigella sonnei isolates from Bhutan.
- To investigate the genetic relatedness and resistance mechanisms of these isolates.
Main Methods:
- Antimicrobial susceptibility testing (disc diffusion, MIC assays).
- Pulsed-field gel electrophoresis (PFGE) and plasmid profiling.
- DNA sequencing of gyraseA gene and integrons; PCR-based replicon typing (PBRT).
Main Results:
- All 29 Shigella sonnei isolates were multidrug-resistant, exhibiting resistance to ciprofloxacin, nalidixic acid, trimethoprim-sulfamethoxazole, streptomycin, and tetracycline.
- Isolates possessed class 2 integrons (dfrA1, sat1, aadA1) and specific mutations in Gyrase A (Ser83Leu, Asp87Gly), conferring quinolone resistance.
- PFGE and plasmid analysis indicated a clonal relationship among isolates, with common ColE plasmids co-residing with B/O or I1 plasmids.
Conclusions:
- The Shigella sonnei isolates from Bhutan in 2011 demonstrated identical PFGE, plasmid, and resistance patterns.
- These findings suggest a clonally related, multidrug-resistant population of Shigella sonnei in the region.
- This underscores the importance of continued monitoring for antimicrobial resistance in enteric pathogens.
