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) . 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).
Processing of stool samples from the patients with identification of NDM1 was performed because Enterobacteriaceae are gut commensal organisms, and their carriage may pose a risk of dissemination in the community. A total of 10 patients were available for stool screening for NDM1 at 1 month after completion of treatment. None of the Enterobacteriaceae isolates from the stool samples were carbapenem resistant.
The development pipeline for antibiotics against gram-negative bacteria is dry, and no new drugs are available. Colistin and tigecycline are the only available agents for treatment of patients infected with gram-negative organisms, and both agents have limitations. Rational use of carbapenems with rapid de-escalation is urgently required. Stringent infection control in hospitals is needed to limit the spread of these organisms.
We thank David Livermore and NeilWoodford (Antibiotic Resistance Monitoring and Reference Laboratory, United Kingdom), for their input.
Financial support. National Health and Education Society; P. D. Hinduja National Hospital and Medical Research Centre.
Potential conflicts of interest. All authors: no conflicts.