A Highly Promiscuous Integron, Plasmids, Extended Spectrum Beta Lactamases and Efflux Pumps as Factors Governing Multidrug Resistance in a Highly Drug Resistant Isolate BD146 from Kolkata, India.

In an earlier study from this laboratory, BD146, a clinical isolate from Kolkata, India, 2002, was found to be resistant to all the fourteen antibiotics tested. It harboured a high copy number plasmid pBD146 and a low copy number plasmid. In the present study, a more detailed analysis was carried out to unravel different resistance mechanisms in this isolate. Sequencing showed that variable region of class 1 integron located on low copy number plasmid harbored 3-A--A1 gene cassettes. Analysis for extended spectrum beta lactamases (ESBLs) revealed that BD146 was ESBL positive. Efflux pumps were involved in the drug resistance phenotype for chloramphenicol, kanamycin, streptomycin and tetracycline. Sequence analysis of pBD146 revealed the presence of genes encoding an integrase with a unique sequence having little similarity to other known integrases, toxin-antitoxin (), a replicase, trimethoprim resistance () and quinolone resistance (). Presence of A, putative novel integrase and toxin-antitoxin system in has been documented for the first time in this report. pBD146 showed 99% sequence similarity with pVN84 from O1 of Vietnam, 2004 and a plasmid from v110 of Hong Kong, 2010. Conjugation experiments proved the ability of pBD146 and the low copy number plasmid, to get transferred to another host imparting their antibiotic resistance traits to the transconjugants. Therefore, present study has indicated that plasmids played an important role for dissemination of drug resistance.