Background: New Delhi metallo-b-lactamase-1 (NDM-1) is a relatively recent carbapenemase enzyme that inactivates all b-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.
Molecular Detection Of The New Delhi Metallo-B-Lactamase-1 Gene In Enterobacteriaceae Isolates In A Tertiary Medical Centre

Aims: Proteus species are implicated as serious causes of various human infections. Imipenem has been used to treat infections caused by these organisms. However, Proteus spp. are known to have reduced susceptibility and have elevated minimum inhibitory concentration (MIC) towards imipenem. The aim of this study was to determine the prevalence of Proteus species with reduced susceptibility to imipenem and the antibiotic susceptibility pattern for each Proteus species. Methodology and results: A total of 204 Proteus isolates were collected from routine samples. All isolates were identified by using VITEK® 2 GN ID card. Antibiotic susceptibility tests were done by using disc diffusion method and imipenem E-test. While 5.9% of the Proteus isolates showed reduced susceptibility towards imipenem by disc diffusion, only 1% (2 out of 204 isolates) has reduced susceptibility by E-test. Conclusion, significance and impact of study The prevalence of Proteus species with reduced susceptibility to imipenem is still low. The imipenem zone diameter does not truly reflect the MIC value and thus, in any isolates which are tested to have reduced susceptibility or resistant to imipenem should always be followed by imipenem MIC method.