Abstract
We studied the molecular mechanism of resistance in extended-spectrum,beta-lactamase (ESBL)producing Klebsiella pneumoniae isolated from a neonatal intensive care unit (NICU) of one of the hospitals in North India. A total of 3000 clinical samples were collected from a NICU (January 2009 to February 2011), of which 523 strains were K pneumoniae positive and 262 of them were ESBL-producing K. pneumoniae strains. All of the ESBL-producing clinical isolates were susceptible to carbapenems. However, the majority of the clinical isolates (30-96%) were resistant to a wide range of antibiotics including antibiotic/inhibitor combinations. The MIC values confirmed that these isolates were highly resistant to cephalosporins and aztreonam. In the 262 ESBL-producing K. pneumoniae isolates, 15 different enterobacterial repetitive intergenic consensus (ERIC)-PCR-typed phylogenetic groups were identified and reconfirmed by PFGE. Characterization of plasmids from each representative member of these phylogenetic groups revealed the presence of three plasmids of different sizes. Conjugation experiments confirmed the presence of different resistance markers only on the 154 kb plasmid. PCR amplification and sequence analysis revealed that bla(CTX-M-3), bla(TEM-1), bla(SHV-1), bla(OXA-1) and armA were the predominant resistance markers. Plasmid-replicon typing showed that Incl1-I gamma and IncFIA-FIB types are the most prevalent. This study shows the co-existence of multiple ESBL-encoding genes and their polyclonal dissemination among K. pneumoniae clinical isolates in the NICU of a North Indian hospital.