The causes and effects of antibiotic resistance

Essay by kaviHigh School, 12th gradeA, August 2007

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The causes and effects of antibiotic resistanceThe development of antibiotic resistance in bacteria is an example of the process of natural selection.Bacteria, like all organisms, are genetically variable. These variations occur by natural mutation giving rise to new alleles of genes. Natural selection can change the frequency of these alleles in the population so that most of the bacteria in the population are resistant, by the following steps:• Within natural populations of bacteria, some individuals have alleles of genes which give resistance to a particular antibiotic• bacteria cause an infection, leading to treatment of the infected person with antibiotic• the antibiotic will kill susceptible bacteria, but resistant bacteria will survive• only the resistant bacteria will reproduce, resulting in an increase in the frequency of the bacteria that are resistant to that particular antibiotic• there will be an increase in allele frequency for the allele of the gene that gives resistance in the population of bacteria• people infected in the future are infected by bacteria more likely to carry the alleles for resistanceDuring the second half of the twentieth century, there was an increasing and widespread use of a whole range of antibiotics.

The result has been that many strains of bacteria have been established which are resistant to a variety ofantibiotics.

The alleles of genes that cause resistance arise for the first time by mutation. Such genes are often located on plasmids, which means that they can rapidly spread fromone bacterial species to another since plasmids arenaturally exchanged between species. The plasmids may also contain a number of different antibiotic resistancegenes so that species can suddenly acquire resistance to a number of antibiotics when before they had none. Such populations of bacteria that are now resistant to anumber of different antibiotics, may cause infections that are extremely...