by R. Cunningham

Created on: May 16, 2009

What Doesn't Kill Them Makes Them Stronger

Certain bacteria develop a resistance to antibiotics, causing a super bug, like MRSA, to develop. It is a textbook example of natural selection and evolution in action. Antibiotic resistance occurs when a few bacteria in a large population of bacteria develop a genetic mutation that renders them less sensitive to the antibiotic. These bacteria that are not killed by the antibiotic reproduce and, due to the elimination of the bacteria without the mutation in the past generation, the new generation contains more bacteria that have resistance against the antibiotic. At the same time, new mutations occur in each generation, contributing to even more genetic variation. Although advantageous mutations are extremely rare, populations of bacteria are large enough and reproduce quickly enough that a few individuals will have beneficial mutations. If a new mutation reduces their susceptibility to an antibiotic, these individuals are more likely to survive when once again confronted with that antibiotic. Given enough exposure to the antibiotic, a population of antibiotic-resistant bacteria will eventually emerge.

This method of survival by the bacteria is called natural selection. Natural selection is the process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common. It is the mechanism through which evolution takes place in a population of a specific species. Natural selection occurs through sexual reproduction, genetic mutation, and genetic recombination which all cause genetic variation in a species. Under certain environmental conditions, these genetic variations give advantages for better survival upon individuals with certain genetic combinations. When this happens, those individuals will thrive and reproduce more than other organisms. In the scenario of the bacteria, those bacteria that can resist that antibiotic have a greater chance of survival than those that are susceptible to the antibiotic. Susceptible bacteria are killed or inhibited by an antibiotic, resulting in a selective pressure for the survival of resistant strains of bacteria.

The biggest cause for this problem is widespread use and misuse of antibiotics. The more antibiotics that are used, the more bacteria will mutate in order to resist it. It has gotten to the point that certain strains of bacteria have been deemed "superbugs" because of their invulnerability to existing drugs. Yet, scientists have been working hard to find a solution to this problem. Response strategies typically include the use of different, stronger antibiotics. However, new strains of certain viruses have emerged that are resistant even to these drugs. It is important for researchers to study how the mutations that give rise to resistance occur, exactly what those mutations are, and how they work. Through this research on the mutations themselves, they can hopefully determine what can be done to counteract them. Perhaps even more important is formulating a strain of antibiotics that has the ability to mutate simultaneously along with the bacteria. In the meantime, avoiding using antibiotics unnecessarily is the best bet to protect the power of existing anti-microbial weapons and slow the inevitable rise of resistance.

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