Spread of Enterobacteriaceae with a New Resistance Gene

Enterobacteriaceae with carbapenem resistance conferred by New Delhi metallo-β-lactamase-1 (NDM-1) were first identified in 2008 in a patient from Sweden who had undergone surgery in New Delhi. To characterize such resistance and assess its distribution, investigators screened resistant Enterobacteriaceae isolates from India and the U.K. for this enzyme. The study was conducted with partial support from Wyeth, which manufactures tigecycline (1 of the 2 antibiotics sometimes effective against these multiresistant bacteria).

Among 141 carbapenem-resistant Enterobacteriaceae isolates from Chennai, India, 44 (including 19 Escherichia coli and 14 Klebsiella pneumoniae) were NDM-1 positive. Of 47 carbapenem-resistant isolates from Haryana, India, 26 (all K. pneumoniae) were NDM-1 positive. Most of the isolates from Chennai and Haryana were from patients with community-acquired urinary tract infections, pneumonia, or bacteremia. All NDM-1–producing isolates were resistant to multiple antibiotic classes. Polymerase chain reaction testing confirmed the presence of bla-_NDM-1 (the gene encoding NDM-1) — in carbapenem-resistant Enterobacteriaceae from several other cities in India, Pakistan, and Bangladesh.

The number of carbapenemase-producing Enterobacteriaceae referred by U.K. microbiology laboratories to the national reference laboratory increased rapidly in 2008 and 2009; NDM-1–producing isolates, referred from 25 laboratories, accounted for 44% (32 of 73). Of the 29 source patients in the U.K., at least 17 had traveled to India or Pakistan during the previous year, and 14 had been hospitalized there for reasons such as renal or bone marrow transplantation, dialysis, and cosmetic surgery. In India, bla-_NDM-1 was carried only on plasmids; in three U.K. isolates, it was also carried on bacterial chromosomes. In the laboratory, the gene transferred readily to other bacteria.