Molecular characterization of multidrug-resistant Shigella species isolated from epidemic and endemic cases of shigellosis in India

1 National Institute of Cholera and Enteric Diseases, Kolkata, India 2 Department of Chemistry, Bose Institute, Kolkata, India 3 Department of Microbiology, Post Graduate Institute of Basic Medical Sciences, Chandigarh, India 4 Osaka Prefecture University, Osaka, Japan Correspondence Thandavarayan Ramamurthy tramu{at}vsnl.net Received 18 January 2008 Accepted 19 March 2008 Shigella species represent one of the growing numbers of antimicrobial-resistant bacteria in developing countries. Fluoroquinolone-resistant strains of Shigella dysenteriae type1 and Shigella flexneri type 2a emerged in India during 2002 and 2003, respectively. Sixty strains of Shigella from different parts of India were analysed for antimicrobial susceptibility, the presence of the qnr plasmid, mutations in the quinolone resistance determining regions (QRDRs), fluoroquinolone accumulation, and the presence of other genes encoding resistance to various antimicrobials. Fluoroquinolone-resistant strains had mutations in gyrA and parC genes and had an active efflux system. They were also resistant to several other antimicrobials but were susceptible to azithromycin and ceftriaxone. The majority of the strains harboured genes encoding resistance to ampicillin (97 %), tetracycline (95 %), streptomycin (95 %) and chloramphenicol (94 %). PFGE analysis revealed clonality among strains of S. dysenteriae types 1 and 5, S. flexneri type 2a and Shigella boydii type 12. Abbreviations: CCCP, carbonyl cyanide m -chlorophenylhydrazone; QRDR, quinolone resistance determining region. The GenBank/EMBL/DDBJ accession numbers for the bla CTX-M-3 sequence of S. boydii type 1, the aac(6')-Ib-cr sequence of S. flexneri type 3b, the aac(6')-Ib-cr sequence of S. boydii type 1 and the gyrA and parC sequences for S. boydii type 1 are EF077620, EF501990, EF501993, EF077618 and EF077619, respectively.