The recent media interest in the superbug is based on an article published in a medical journal from UK.
In a study on a group of bacteria called Enterobacteriaceae (commonly found in the gut), researchers claim that resistance to carbapenems conferred by NDM-1 is a potential major global health problem. They studied the prevalence of NDM-1 in multidrug-resistant organisms belonging to the Enterobacteriaceae group isolated from patients in India, Pakistan and the UK. The bacterial isolates were studied from two major centres in India – Chennai and Haryana, and those referred to the UK’s national reference laboratory. Antibiotic sensitivity was tested to check which antimicrobials would be effective in their treatment, and they also looked for the gene encoding NDM-1 in these bacterial isolates. These were further subtyped to find out if they were related or not by various techniques. The details of patients from UK were reviewed to check for travel and recent admission to hospitals in India or Pakistan.
From the large group of organisms studied, they found 44 isolates with NDM-1 in Chennai, 26 in Haryana, 37 in the UK, and 73 from other sites in India and Pakistan. NDM-1 was mostly found among Escherichia coli (36) and Klebsiella pneumoniae (111), which were highly resistant to all antibiotics except to tigecycline and colistin. Based on experiments in the lab they found that the gene producing NDM-1 can move from one bacterium to another, thus transferring the resistance property.
Many of the NDM-1 positive patients from UK had travelled to India or Pakistan within the past year, or had links with these countries, though these details were neither mentioned nor analysed for statistical significance. No travel history of patients from India was obtained, and screening of the UK patients before their travel was not done to find out if they had been harbouring these bacteria before they visited India or Pakistan. On the basis of genetic tests in the lab, they could not prove conclusively that the Indian & UK isolates were related. The declared conflict of interest by the authors mentions support from a pharmaceutical company that manufactures an antimicrobial that may be effective in managing these infections.
Based on this article, the media has sensationalised the resistance property of these drug resistant organisms by calling them a superbug. It is difficult to comprehend how a reputed peer-reviewed journal could publish the over-reaching conclusions of the authors, without definite evidence that these strains originated from India, as well as strongly advise against UK patients coming for surgery to India.
This study could have serious repercussions on medical tourism to India and Pakistan, despite the fact that resistance can emerge in any country and resistant organisms do not recognise national borders. Instead of pointing fingers, there is a need to work together towards monitoring antimicrobial resistance and prudent use of antimicrobials at all levels - global, national and local.
Background
The superbug is not a single organism or an enzyme, but a group of organisms, commonly found in the human gut, which have developed resistance to some broad spectrum antimicrobials, thereby posing a treatment challenge.
All micro-organisms (commonly called bugs) have the evolutionary potential to change in response to their environment. Bacteria exposed to antimicrobials (also known as antibiotics) either in the environment or during treatment undergo changes (develop resistance) to either withstand or neutralise the effect of these antimicrobials through enzymes. This can happen through mutation in their genes and this protective property acquired by the bacteria can be passed on to subsequent generations, thereby protecting them from the effect of the antimicrobials.
Some common drug-destroying enzymes that confer resistance in bacteria include:
- Penicillinase – destroys pencillin
- ß-lactamases – confer resistance against some antimicrobials of the penicillin and cephalosporin groups
- Extended spectrum ß-lactamases (ESBLs) – confer resistance against broad spectrum cephalosporins
- Metallo-ß-lactamases (MBLs) – confer resistance against carbapenems (a group of potent, broad spectrum antimicrobials
Why NDM?
A type of metallo-
ß-lactamase isolated from drug resistant bacteria was surprisingly called New Delhi metallo-
ß-lactamase-1 (NDM-1). This was first isolated in an organism from a patient of Indian origin living in Sweden for many years who had visited India and then gone back to Sweden. However, there is no information whether he was harbouring the drug resistant bacteria when he came from Sweden. Though KPC (
Klebsiella pneumoniae carbapenemase) was first isolated in an organism from a patient in New York, it was not labelled as New York carbapenemase! Mexico had taken strong exception to the pandemic H1N1 flu being called the Mexican flu in the media, even though the initial cases were reported from their country.
Reference:
The Lancet Infectious Diseases, August 2010