New Delhi Metallo 1: Have Carbapenems Met Their Doom?

To the Editor—Carbapenems are the most potent antibiotics used to treat sepsis. High-level resistance to carbapenems ismediated by hydrolysis of the drugs by carbapenemases. Carbapenem-resistant Pseudomonas and Acinetobacter species have been described extensively [1, 2]. The recent emergence of a new carbapenemase, the New Delhi metallo 1 (NDM1) enzyme, has been linked to the Indian subcontinent and is accumulating among organisms, possibly because of efficient plasmid transfer. From September 2009 through May 2010, 310 carbapenem-resistant gram-negative bacilli were isolated from clinical samples at our tertiary care center. These consisted of Enterobacteriaceae (57), Pseudomonas species (173), and Acinetobacter species (71). The incidence of carbapenem resistance among Enterobacteriaceae was 5.3% in blood isolates, 7.81% in respiratory tract isolates, and 5.27% in urine isolates. We phenotypically identified carbapenem- resistant organisms by the modified Hodge test and molecularly identified NDM1 in 49 of 57 Enterobacteriaceae isolates, comprising Klebsiella species (28), Escherichia coli (13), Enterobacter species (5), Morganella morganii (2), and Citrobacter species (1) [3]. All patients had received treatment with carbapenem in the past month. Other associated risk factors were indwelling invasive devices, such as urinary catheters (67% of patients) and central venous catheters (54%), and severe illness (63%). There were 8 carbapenemresistant isolates that were nonproducers of NDM1 (they may have been producers of Klebsiella pneumoniae carbapenemases or other metallo-β-lactamases).