Molecular analysis of multidrug resistance in clinical isolates of spp. from 2001-2010 in Kolkata, India: role of integrons, plasmids, and topoisomerase mutations.

To understand the genetic basis of high drug resistance in , 95 clinical isolates of spp. (2001-2010) were obtained from the Infectious Diseases Hospital, Kolkata, India. Ninety-three isolates were resistant to three or more antibiotics. Resistance to nalidixic acid, trimethoprim, streptomycin, and co-trimoxazole was most common in this population. Dendrogram analysis showed that strains were more clonally related when compared to the other species. The role of mobile genetic elements and chromosome-borne resistance factors was analyzed in detail. Integron analysis indicated the preponderance of class 2 and atypical class 1 integrons in that population. Typical class 1 integron was present in only one isolate and harbored trimethoprim resistance-encoding gene , while atypical class 1 integrons harbored or gene cassettes responsible for resistance to trimethoprim, aminoglycosides, and β-lactams. Class 2 integrons harbored either or gene cassettes. Most importantly, a novel gene cassette array was found in class 2 integron of NK4846. Many of the resistance traits for antibiotics such as trimethoprim, co-trimoxazole, kanamycin, ampicillin, and tetracycline were transferred from parent isolates to recipient during conjugation, establishing the role of plasmids in horizontal transfer of resistance genes. Multiple mutations such as S→I, S→L, and D→G/N/Y in quinolone resistance determining regions of topoisomerases from the representative quinolone-resistant isolates could explain the spectrum of minimal inhibitory concentration values for various quinolones. To the best of our knowledge, this is the first comprehensive report that describes the contribution of mobile (plasmids, integrons, and quinolone resistance genes named qnr) and innate genetic elements (mutations in topoisomerases) in determining the resistance phenotype of all the four species of over a span of ten years.