Abstract
Objective:The New Delhi metallo-β-lactamase-1 (NDM-1) enzyme is a plasmid-encoded enzyme that inactivates carbapenem antibiotics. This study aims to ascertain if the modified Hodge test (MHT) has a role in screening for NDM-1 in Enterobacteriaceae with reduced carbapenem susceptibility.Methods:Over a period of one year, all Enterobacteriaceae isolates from all clinical specimens with reduced susceptibility to at least one carbapenem were subjected to MHT and conventional polymerase chain reaction (PCR) detection of the NDM-1 gene.Results:A total of 13,098 Enterobacteriaceae isolates were screened and 63 (0.48%) had reduced susceptibility to at least one carbapenem. Out of the 63 isolates, 45 (71.4%) were MHT-positive. The NDM-1 gene was detected in 18 of the 63 isolates (28.6%). All 18 PCR-positive isolates were also MHT-positive. Thus, the sensitivity and specificity of the MHT in detecting NDM-1 in Enterobacteriaceae with reduced carbapenem susceptibility are 100% and 40%, respectively.Conclusion:The MHT is a useful test to screen for the presence of NDM-1 in Enterobacteriaceae with reduced carbapenem susceptibility. However, due to its rather low specificity, all MHT-positive isolates should be subjected to alternative tests (e.g. PCR) for confirmation, especially if other types of carbapenemases (e.g. KPC) are prevalent.
Highlights
New Delhi metallo-β-lactamase-1 (NDM-1) is a carbapenemase enzyme that hydrolyzes all β-lactam antibiotics except aztreonam
Screening for carbapenem resistance: Screening was carried out by disk diffusion according to the recommendations in the Clinical and Laboratory Standards Institute (CLSI) document M100-S24.3 The carbapenem antibiotic disks used for each isolate were ertapenem (10mg), imipenem (10mg), meropenem (10mg) and doripenem (10mg)
Prior to 2015, the modified Hodge test (MHT), which is known as the cloverleaf test, was the only phenotypic confirmatory test for carbapenemase production in Enterobacteriaceae described by the CLSI.[3]
Summary
New Delhi metallo-β-lactamase-1 (NDM-1) is a carbapenemase enzyme that hydrolyzes all β-lactam antibiotics except aztreonam. It was first described in 2008 in a 59-year-old Swedish patient when he was hospitalized for a urinary tract infection in New Delhi, India.[1] Many NDM1-positive isolates harbour other resistant genes and pose major therapeutic dilemmas. Few new antimicrobials are in the pipeline to be used against carbapenem-resistant Enterobacteriaceae. The NDM-1 gene is readily transferable to other bacteria.[2] it is important to screen for NDM-1 production in Enterobacteriaceae so that rapid infection control measures can be instituted
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