by Alicia M Prater PhD

Created on: August 16, 2010   Last Updated: October 29, 2010

NDM-1 stands for New Delhi metallo-beta-lactamase-1, a new bacterial gene discovered in 2009 (see Yong et al.) The gene encodes an enzyme known as metallo-beta-lactamase. In this case, the new subgroup of enzymes made by the gene are carbapenemases – they act against this specific class of antibiotics, making bacteria that express these enxymes carbapenem-resistant. Single resistant bacteria have been around for a long time, but the new gene is found alongside other resistance genes and the carbapenems are a very important family of antibiotics. So far, multiple resistance in the presence of NDM-1 has been found in Klebsiella pneumoniae, giving this strain an ability to withstand nearly all available medical treatments for bacterial infections.

Carbapenem Resistance

Carbapenems are considered to be the most powerful class of antibiotics available to medical science. They are the last line of defense against antibiotic-resistant Enterobacteria, a family of bacteria that includes E. coli. Carbapenem-resistant bacteria have appeared in recent years carrying the gene that encodes the enzyme KPC. In March 2009, the CDC in the United States issued a warning with recommendations for treating and reporting infections with carbapenem-resistant Klebsiella pneumoniae (CRKP), a type of enterobacteria. In 2007, CRKP represented 8% of all Klebsiella infections and were associated with higher rates of death and complications. In 2008 and 2009 the UK had similar warnings.

The Spread of NDM-1

In 2010, bacteria carrying NDM-1 are now known to be spread throughout India. Bacteria containing the gene have been reported in the UK because of patients who travel abroad for medical procedures, as well as the United States, Canada, and Australia. The New Delhi gene is becoming a common variant in the bacterial genome, and is currently found in an estimated 1 to 3 percent of enterobacteria infections (NewScientist). So far the resistant bacteria still appear to respond to polymyxins and tigecycline, though the latter is not consistent.

How NDM-1 Affects Treatment

The trouble with this new gene is two-fold. First are the problems with any resistance gene - resistance can spread from this bacterial strain to another by horizontal gene transfer. Bacteria shuttle genetic sequences back and forth with one another, allowing resistance to spread simply by the presence of a single resistant bacterium in a population. This gene occurs as such a unit, a cassette in the bacterial plasmid.

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