The threat of superbug NDM-1
Gram-negative Enterobacteriaceae strains resistant to carbapenem, a powerful antibiotic, and one of the last lines of treatment for infections caused by Gram-negative bacteria, are becoming more widespread in India. The resistance arises on account of a new gene that codes for metallo-beta-lactamase enzyme. The drug-resistant bacterial gene, the so-called superbug, was named New Delhi metallo-beta-lactamase-1 (NDM-1) in 2009 when it was first identified in a Swedish person admitted to a hospital in New Delhi.
A study, reported online in The Lancet Infectious Diseases, found that apart from several locations in India, the carbapenem-resistant strain was seen in 37 U.K. patients who had undergone elective and cosmetic surgery in India and two neighbouring countries. According to a study published in March in the Journal of Association of Physicians of India (JAPI), 22 cases of carbapenem-resistant NDM-1 were collected within three months from a Mumbai hospital.
The spread and increasing numbers come as no surprise as the drug is overused. Resistance to extended-spectrum beta-lactamases (ESBL) drugs like third-generation cephalsporins is between 60 and 70 per cent on average in India, compared with less than 15 per cent seen in many developed countries. A common way of treating the severe form of ESBL infections is the use of carbapenem — which becomes the drug of choice as it has the lowest resistance rates and the broadest action against Gram-negative infections.
Inappropriate and indiscriminate use of carbapenem, a reserved antibiotic, has played a major role in the development of the carbapenem-resistant gene, including the new NDM-1 strain. From being absent a few years ago, NDM-1 is beginning to show up. Unlike ESBL, which has become a community infection, NDM-1 is, in all probability, still a hospital-acquired infection. Drug-resistant NDM-1 strains are being seen only now but they are a cause for worry because only a few drugs are available to treat Gram-negative infections. The prevalence can increase within a relatively short time, since the NDM-1 gene is carried in the plasmids of the Gram-negative bacteria. These plasmids can move from one bacterium to another, and even to different species.
There is still a good chance of keeping the prevalence low, provided a two-pronged approach is adopted: instituting a national antibiotic policy that restricts the use of carbapenem and other higher-end antibiotics to hospital settings and only for patients with severe infections, and having a national registry of drug-resistant strains.
Published in The Hindu on August 16, 2010
