16 August 2010
How do bacteria develop resistance to a drug?
If a group of bacteria is exposed to some antibiotic, it is possible that a few of them will possess a better survival and reproduction mechanism than the others. This information stored in a bacterium’s gene (unit of heredity) can pass on to the other members of the group and continuation of the process can ultimately result in the development of complete resistance against the particular antibiotic in all members of the group. If a bacterium carries several resistance genes then it becomes multi–resistant, commonly known as a ‘superbug’.
What factors increase the rate of development of drug resistance?
It is generally observed that a larger duration of exposure to an antibiotic increases the risk of development of resistance. The widespread use of antibiotics has played an important role in evolution of the drug resistant bacterium. Apart from being used as medicine for humans, antibiotics are also used on farm animals either to treat diseases or for promoting growth, which increase the exposure of bacteria to the drug.
Inappropriate treatment, overuse, self–prescription, failure in completing the prescribed course and misuse like taking antibiotics to treat common colds, which is actually a viral infection – result in the undue exposure of bacteria to the drug facilitating the evolution of antibiotic–resistant population. It is also observed that the inappropriate disposal of pharmaceutical industry waste may result in environmental pollution with broad spectrum antibiotics helping bacteria develop resistance.
When was the now–famous ‘superbug’ discovered?
After unsuccessful treatments in hospitals in Ludhiana and New Delhi, a 59– year–old Swede of Indian origin was referred back to a Swedish hospital, where it was discovered that he had acquired an antibiotic–resistant bacterial infection during his stay in India. The cause of the infection was later described in a December 2009 paper published by Yong et al.
The bacteria was the host to a gene which initiates the production of an enzyme called NDM–1 (New Delhi metallo–beta–lactamase–1). This enzyme can chemically break down carbapenem antibiotics, which are seen as a last–resort antibiotic to treat severe bacterial infection. A March 2010 study of a Mumbai hospital also pointed towards the presence of the NDM–1 gene in anti–carbapenem bacteria isolated from patients.In May 2010 the same gene was found in a case detected in the UK and three cases were detected in the US in June 2010. This resulted in a multinational study.
Its results, published in August 2010, pointed towards 37 anti–carbapenem cases in the UK, 44 in Chennai, 26 in Haryana and 73 in various sites in Pakistan and India, all having the NDM–1 gene.
Considering the connection with India and Pakistan in the patients, international experts believe that the gene originated in India – a claim that is disputed by the Indian government which calls it unfair to associate India’s name with it. So far two types of bacteria have been found host to NDM–1 – E.coli and the bacteria which causes Klebsiella pneumonia.
Why has it caused alarm?
Experts are alarmed because the enzyme can make bacteria resistant to most last–resort drugs, leaving little hope of successful treatment. Second, the gene is found to be capable of easy replication in other strain of bacteria which may result in the formation of another superbug, resistant to many other antibiotics.
This can cause dangerous infections which would spread rapidly from person to person. Third, there are not many drugs under pharmaceutical industry research programmes which can address drug resistance in pathogens. Since it takes several years to develop and commercialize drugs, there is fear that the NDM–1 carrying superbug may spread, with no cure available.