New Delhi Metallo-Beta-Lactamases -1 in a tertiary care pediatric center

Background:  Emergence of antimicrobial resistance is natural process which is further accelerated due to indiscriminate use of antimicrobials. The New Delhi metallo-β-lactamase (NDM-1) first described 2009 in Sweden has recently been found in patients worldwide. The gene is now widespread found in K. pneumoniae, Escherichia coli  and Acinetobacter baumannii in India and has been reported recently to occur in USA, Europe and Japan.

Objective:  To determine prevalence of Multi-drug Resistant Organisms (MDROs), Extensively drug resistant organisms (XDROs) and Pan Drug Resistant Organisms (PDROs) in a tertiary care pediatric center. The study also evaluated detection of genes encoding NDM-1 in such isolates through real time PCR.

Methods:  The study was conducted on the clinical isolates obtained during January to June 2010. Bacterial strains obtained from clinical specimens submitted to the clinical microbiology laboratory at Chacha Nehru Bal Chikitsalaya (CNBC), Delhi were included. Definitions included Gram -negative bacilli (GNB) that are resistant to all cephalosporins and inhibitor combinations, fluoroquinolones and aminoglycosides but sensitive to carbapenems and colistin (MDROs), MDROs that are resistant to carbapenems (XDROs) and XDROs resistant to polymyxins also (PDROs).The clinical strains that were resistant to carbapenems that were screened positive by modified Hodge test and disk synergy (EDTA with Imipenem) were further subjected to NDM-1 detection using real time PCR using taqman chemistry. E. coli ATCC 25922 and Klebsiella pneumoniae ATCC 700603 were also included as negative controls.  Primer and probe sequences were derived from Genbank sequence AB571289. The assays were optimized using a cloned synthetic gene fragment covering the region 35-366.

Results: During the study period of January to June 2010, a total of 383 GNB were isolated. Among these isolates 81 GNBs were MDROs (21%). A total of 36 MDROs revealed XDROs antimicrobial susceptibility pattern. No PDROs were isolated during this period. Among the strains tested for NDM-1 gene, two strains of Escherichia coli and six strains Klebsiella pneumoniae were found harbouring NDM-1 gene.

Conclusions:  Significant numbers of clinical isolates were MDROs and were equally spread to community and hospitals. XDROs were largely confined to hospital setting with none of the NDM harbouring isolates from out-patient department. Implementation and monitoring of antimicrobial stewardship program can decrease rate of emergence of such organisms in community.