NDM-1, or New Delhi metallo-ß-lactamase-1, is an enzyme that can confer resistance to certain gram negative bacteria like E.coli and Klebsiella against a class of antibiotics called carbapenems.
Of particular concern, the gene (blaNDM-1) that encodes this enzyme is carried by a plasmid – a snippet of portable DNA - that can be horizontally transferred to other types of bacteria (see Study: Adaptation Of Plasmids To New Bacterial Species).
The NDM-1 enzyme made headlines last August when a Lancet Infectious Diseases article was published on its growing prevalence on the Indian sub-continent and its recent importation into the UK, US, and other countries.
In April of 2011, the same researchers published a new study (again in The Lancet) that found the NDM-1 enzyme in 4% of New Delhi’s sampled drinking water sources, and 30 per cent of the sewage tested (see Lancet Study: NDM-1 In New Delhi Water Supply) and perhaps most importantly – identified 11 new species of bacteria carrying the NDM-1 gene, including strains which cause cholera and dysentery.
While there have been scattered instances of NDM-1 bacterial infections detected in the United States and in Canada, practically all of them can be traced back to travel to India or Pakistan.
Today’s report in the Canadian Medical Association Journal highlights two cases of NDM-1 urinary tract colonization in Canada. In each case the patients were asymptomatic, no further spread (in-hospital or to family contacts) was detected, and antibiotics were withheld to avoid giving the bacteria an opportunity to develop further resistance.
One subject had recently traveled to India, while the other had not traveled outside of Ontario for at least 10 years and is believed to be the first documented instance of local acquisition of NDM-1.
Additionally, both cases involved bacterial strains (Morganella & Providencia) not normally associated with NDM-1, and both cases illustrate the difficulties in identifying organisms that produce NDM-1 with current laboratory testing protocols.
You can read the details in:
Julianne V. Kus, Manal Tadros, Andrew Simor, Donald E. Low, Allison J. McGeer, Barbara M. Willey, Cindy Larocque, Karen Pike, Iris-Ann Edwards, Helen Dedier, Roberto Melano, David A. Boyd, Michael R. Mulvey, Lisa Louie, Christopher Okeahialam, Mark Bayley, Cynthia Whitehead, Denyse Richardson, Lesley Carr, Fatema Jinnah and Susan M. Poutanen
Today’s report should not inspire undo public alarm, as the risk to the public is very low. This should, however, serve as a reminder to hospitals and health care facilities that NDM-1 is a growing concern.
Doctors will now have to consider that a history of recent foreign travel, while still the most common route of NDM-1 acquisition in North America, is no longer a firm prerequisite for infection.
And hospitals will have to gear up to deal with the the patient screening and infection control challenges that a new resistant pathogen presents, while laboratories will have to develop new testing protocols.
The NDM-1 enzyme was first identified in a Klebsiella pneumoniae isolate from a native of India, who was then a resident in Sweden, just three years ago. Since then it has been detected in bacteria in India, Pakistan, the United Kingdom, the United States, Canada, Japan and Brazil.
While the end of the antibiotic era is not yet at hand, the fear is we may be drawing closer to that day. Which is why we watch reports of bacterial resistance with such great interest.
And Maryn’s SUPERBUG Blog, now part of Wired Science Blogs, continues to provide the best day-to-day coverage of these issues.