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Background. Carbapenem resistance among Gram-negative isolates caused by the production of the metallo-β-lactamase (MBL) enzyme is being increasingly reported worldwide. One of the newly emerged metallo-β-lactamases is New Delhi metallo-β-lactamase. Data regarding its occurrence in hospital setting and percentage prevalence among different Gram-negative bacterial isolates are lacking in our part. This study has been undertaken for determining the presence of the bla NDM-1 gene among the clinical isolates of imipenem-resistant Gram-negative bacteria in a tertiary care center in Dharan, Nepal. Methods. A total of 75 imipenem-resistant Gram-negative isolates were studied. These were screened for metallo-β-lactamase (MBL) production by phenotypic assays such as double-disc synergy test (DDST) and combined disc diffusion test (CDDT). PCR was performed for the molecular detection of gene NDM-1. Ten-disc method was performed to detect the presence of ESBL, AmpC, carbapenamase, and K1 β-lactamase production. Results. Using the molecular method, bla NDM-1 was detected in 36% of the isolates. Phenotypically, double-disc synergy test (DDST) and combined disc diffusion test (CDST) detected MBL production in 38.7% and 37.3% of the isolates, respectively. Ten-disc method detected ESBL in 26.6% of the isolates, but none of the isolates was found to be AmpC, carbapenamase, and K1 β-lactamase producers. Conclusion. A high percentage of the NDM-1 producer was noted among imipenem-resistant GNB. Apart from performing only antimicrobial sensitivity test, phenotypic and molecular screening should be employed to find out the actual number of metallo-β-lactamase producers and the existence of the resistance gene. [ABSTRACT FROM AUTHOR]

Infections caused by beta-lactamases producing Gram-negative bacteria are increasing, thus posing a challenge to the management of such infections. The surveillance data of such bacteria is limited in Nepal so this study aimed to detect the beta-lactamase producing Gram-negative bacteria in a tertiary setting. A total of 604 clinical samples, including urine, blood, sputum and body fluids, were cultured and identified by the routine standard laboratory protocols. Antibiotic susceptibility testing was done by Kirby Bauer disc diffusion method following Clinical and Laboratory Standard Institute guidelines (2014). Extended-spectrum betalactamases (ESBL) producers were identified by combined disk method and metallo-betalactamases (MBL) producers were identified by Imipenem- EDTA combined disk method. Out of 604 samples, 282 (46.7%) samples showed significant growth, of which 229 (81.2%) were Gramnegative bacteria. Of 229 Gram-negative bacteria, 200 (87.3%) were multidrug resistant, 67 (29.3%) were ESBL producers and 16 (7.0%) were MBL producers. Klebsiella pneumoniae were among higher ESBL producers and Pseudomonas aeruginosa were among higher MBL producers. The findings suggest higher antibacterial resistance among Gram-negative bacteria with the added burden of beta-lactamase production. Imipenem was effective against 125 of 229 Gramnegative bacteria tested. Thus, imipenem can be the drug of choice for empirical management. The higher multidrug resistance and higher beta-lactamases production among Gram-negative bacteria warrant the continuous monitoring, surveillance, early detection, and infection control practices of such bacteria. [ABSTRACT FROM AUTHOR]