Identification of Typical Class 1 and Class 2 Integron Gene Cassettes in Clinical Isolates of MDR Shigella flexneri in South Indian Population

Aims: Shigellosis is an acute intestinal infection caused by Shigella spp. Treatment with most widely used antimicrobial drugs became limited due to the emergence of multi-drug resistance (MDR). In Shigella spp., antimicrobial resistance is often associated with the presence of transferable genetic elements (integrons and plasmids). Therefore, the study was aimed to identify the pattern of integron distribution in clinical isolates of Shigella spp. in south Indian population.

Place and Duration of Study: Department of Clinical Microbiology, Christian Medical College (CMC), Vellore, between January 2014 and December 2014.

Methodology: A total of 20 out of 67 MDR Shigella isolates were included in the study. All 20 isolates were characterized for the presence of integrons, gene cassettes and other resistant genes by PCR, restriction fragment length polymorphism (RFLP) and sequencing. The integron sequences were deposited in NCBI.

Results: The presence of typical class 1 integron gene cassette dfrA12‐orfF‐aadA2 (KT037078) and class 2 integron gene cassette dfr1-sat2-aadA1 (KT037079) from S. flexneri were first to be reported among Indian population in this study. Also, dfrA1‐sat1‐aadA1 gene cassette of class 2 integron along with dhfr1a, sul2,blaOXA, blaTEM, AmpC, blaCTX-M-15 and qnr genes were identified in Shigella spp. in this study.

Conclusion: Association of ESBL, AmpC, blaCTX-M and qnr genes justified the observed phenotypic resistance of the isolates which is of major concern due to the ability of integrons to acquire resistance genes against different antibiotics, since gene cassettes exist to nearly all classes of antibiotics.