Evolution and Antibiotic Resistance

Antibiotics do not, in themselves, cause resistance. Instead, they allow naturally resistant variants within a population to survive and reproduce while those individuals without the resistance factor die. Once in a bacterial population, antibiotic resistance can spread rapidly. Even unrelated bacteria can gain resistance from their neighbors in a phenomenon called horizontal gene transfer (Reece, Simon and Campbell, 2010). Resistance to antibiotics is encoded in DNA, the genetic blueprint for life. Bacteria are able to exchange DNA, especially in the form of plasmids (small, self-replicating circles of DNA) and pass resistance very rapidly.
An antibiotic kills a bacterial cell by simply disrupting a critical function. This is achieved in the cell in much the same way that a saboteur can cause a car to crash by simply cutting the brake lines. Antibiotic resistance of bacteria only leads to a loss of functional systems. Evolution requires a gain of functional systems for bacteria to evolve into man. The antibiotic binds to a protein so that the protein cannot function properly. The normal protein is usually involved in copying the DNA, making proteins, or making the bacterial cell wall—all important functions for the bacteria to grow and reproduce. If the bacteria have a mutation in the DNA which codes for one of those proteins, the antibiotic cannot bind to the altered protein; and the mutant bacteria survive (MacLean, 2010). In the presence of antibiotics, the process of natural selection will occur, favoring the survival and reproduction of the mutant bacteria. (The mutant bacteria are better able to survive in the presence of the antibiotic and will continue to cause illness in the patient.) Although the mutant bacteria can survive well in the hospital environment, the change has come at a cost. The altered protein is less efficient in performing its normal function, making the bacteria less fit in an environment without antibiotics. Typically, the non-mutant...