Adapting by Acquiring Genes

♤ A process known as “horizontal gene transfer*” can also confer drug resistance to bacteria. There are three mechanisms by which horizontal gene transfer can take place: conjugation, transformation and transduction.

♤ Bacteria contain a DNA entity called the ‘plasmid’. Plasmids are circular DNA strands capable of replication independent of the chromosomal DNA. A unique property of plasmids is that copies of replicated DNA can be transferred from one bacterium to another, sometimes even across the species. Known as conjugation, this process is akin to mating in higher organisms. When two bacteria come close to each other, a hollow bridge-like structure called the ‘pilus’ forms between them to facilitate a copy of the plasmid to move from one to another. Plasmids may contain genes that render the bacteria resistant to specific antibiotics. In such a case,the recipient bacteria also become resistant to that antibiotic.

♤ Another means by which bacteria can acquire a readymade resistance gene is a process called ‘transformation*’. When a cell dies, it breaks apart and releases its DNA to the surrounding environment. Bacteria may scavenge these free-floating DNA pieces and incorporate them into their own chromosomes. If the DNA contained an antibiotic resistance gene, the recipient bacteria too can begin to exhibit that property.

♤ A virus may also act as a vehicle for horizontal transfer of genes. Some viruses known as ‘bacteriophages*’ (or simply ‘phages’) are specific to bacteria. When a phage infects a bacterium, it takes over the host biochemical machinery to reproduce itself, ultimately destroying the host. This is known as the lytic phase in the life cycle of the virus.

♤ During this process, known as transformation, the virus may inadvertently incorporate some bacterial genes in to its own genome. Upon the death of the bacterium, the phages infect other bacteria. From the lytic phase the virus enters the lysogenic phase of its life cycle; here the virus will not reproduce in the bacterial cell but integrate its genome with the bacterial genome and replicate along with it. Such bacteria continue to surviveand reproduce, expressing even the viral genes. If the viral genome contained a drug resistance gene, the host bacterium will display resistance to the drug.

The response

♤ One of the fertile targets is the SOS repair pathway as preventing the induction of SOS repair reduces formation of drug resistance not only through chromosomal mutations, but also other mechanisms like horizontal gene transfer and homologous recombination.

♤ However, some researchers feel that such attempts may only extend the time needed for resistance development and will not eliminate the problem completely.

♤ This is because antibiotic antibiotics.

resistance is an unavoidable consequence

of the indiscriminate use of

♤ According to the Food and Drug Administration of the USA, drug resistance “is an outcome of natural selection and should be viewed as an expected phenomenon of the Darwinian biological principle of ‘Survival of the fittest ’”.

♤ As long as the effectiveness of the drug is based on chemical processes, bugs can always develop resistance to the process. Hence, departing from the conventional approach, some researchers are trying to develop next generation antibiotics that may attack bacteria through physical or mechanical means.

♤ Scientists at the IBM research center are developing organic nanoparticles. These particles are so designed that they are physically attracted to the bacteria like a magnet, break through the cell wall.

♤ Researchers at the Gamaleya Institute of Epidemiology and Microbiology, Moscow have some exotic technology in their kitty–cold plasma to kill the bacteria!

How We Help Superbugs Thrive?

♤ There are many situations in which bacteria may find an environment suitable for development of resistance.

♤ When a person is treated with antibiotics, about 30% is absorbed and the rest passes through the body into the sewage system. Antibacterial soaps and disinfectants used in homes and hospitals are also washed into the sewer. Animal breeders mix antibiotics with farm feed, often indiscriminately, to increase the animal’s weight. Such use not only contaminates the meat but also increases the variety and quantity of antibiotics in the sewage.

♤ Antibiotics are not readily degradable. Ultimately the sewage enters a treatment plant, which encourages the growth of bacteria to digest the sewage. During this process, in the presence of low levels of antibiotics, some bacteria may develop resistance. When the digested sludge is dried and used as manure, some of the farm products may get contaminated with bacteria and enter the food chain. In addition, sewers may directly contaminate the drinking water system, as often happens in our country. Both aid the spread of resistant bacteria in the community.

♤ Thus, in a large population of bacteria there may be a few that

have developed resistance to

antibiotics. When an infected person is treated with antibiotics, the susceptible ones perish, leaving behind the resistant ones, which will multiply at the opportune moment. Next time when the same antibiotic is given to the patient, it may not be effective in controlling the infection. When a class of bacteria becomes resistant to a particular drug, the pharmacologist develops a new kind of antibiotic. It takes more than a decade to develop an antibiotic and the bacteria become resistant to even the new drug in due course.

♤ The case of Tuberculosis in India illustrates how various shortcomings in the healthcare system have led to the emergence of Extremely Drug Resistant TB (XDR-TB). Poor compliance of drug course by patients, the tendency of doctors to over-prescribe antibiotics, improper screening of patients and spurious or sub-standard drugs floating around in the market are some of the factors that have led to the strengthening of resistance mechanisms in TB drugs.