Molecular detection of the New Delhi metallo-β-lactamase-1 gene in Enterobacteriaceae isolates in a tertiary medical centre

Background: New Delhi metallo-beta-lactamase-1 (NDM-1) is a relatively recent carbapenemase enzyme that inactivates all beta-lactam antibiotics with the exception of aztreonam. This study aims to ascertain the baseline prevalence and antibiotic susceptibility patterns of NDM-1-producing Enterobacteriaceae in a tertiary medical center in Malaysia. Methods: Over a period of one year, all Enterobacteriaceae isolates from all clinical specimens with reduced susceptibility to at least one carbapenem and resistance to at least one third generation cephalosporin were subjected to antibiotic susceptibility testing by disk diffusion and molecular detection of the NDM-1 gene by single-target PCR followed by gel electrophoresis. Results: A total of 13,098 Enterobacteriaceae isolates were screened and 63 (0.48%) had reduced susceptibility to at least one carbapenem. Of this 63, 18 (29%) were NDM-1-positive. Of this 18, 16 (89.0%) were Klebsiella pneumoniae, one (5.5%) was Escherichia coli and one (5.5%) was Klebsiella ornithinolytica. Reduced susceptibility to at least one aminoglycoside was seen in 17 (94%) of the NDM-1-positive isolates. All 18 (100%) had reduced susceptibility to ertapenem and were resistant to all the second and third generation cephalosporin antibiotics tested. Conclusion: The prevalence of NDM-1-producing Enterobacteriaceae among all the Enterobacteriaceae isolates in our institution is low (0.14%) and screening for the NDM-1 gene is best performed using ertapenem-impregnated disks.