Screening for New Delhi metallo-Beta-lactamase-1 in Enterobacteriaceae: is there a role for the modified Hodge test?

Objective: The New Delhi metallo-Beta-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

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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

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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

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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