How can bacteria acquire antibiotic resistance
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Mutations can result in antibiotic resistance in bacteria. Resistant bacteria survive antibiotic treatment and can increase in numbers by natural selection. Bacteria grow and multiply fast and can reach large numbers. When bacteria multiply, one cell divides into two cells. Before the bacterium can divide, it needs to make two identical copies of the DNA in its chromosome; one for each cell. Every time the bacterium goes through this process there
is a chance (or risk, depending on the end result) that errors occur; so-called mutations. These mutations are random and can be located anywhere in the DNA. Mutations can also form due to external factors like radiation or harmful chemicals. While some mutations are harmful to the bacteria, others can provide an advantage given the right circumstances. Here, Darwin’s theory of natural selection comes in. If a mutation gives the bacterium an advantage in a
particular environment, this bacterium will grow better than its neighbors and can increase in numbers – it is selected for. Mutations are one way for bacteria to become resistant to antibiotics. Some spontaneous mutations (or genes that have been acquired from other bacteria through
horizontal gene transfer) may make the bacterium resistant to an antibiotic (See: Resistance mechanisms for information about how bacteria resist antibiotic action). If we were to treat
the bacterial population with that specific antibiotic, only the resistant bacteria will be able to multiply; the antibiotic selects for them. These bacteria can now increase in numbers and the end result is a population of mainly resistant bacteria. It is important to understand that selection of antibiotic resistant bacteria can occur anywhere an antibiotic is present at a selective concentration. When we treat an infection, selection can occur at any site in the body to which the antibiotic reaches. Thus, the antibiotic can select for resistance genes and mechanisms in both pathogenic bacteria and in commensal bacteria living in the body that have nothing to do with the infection in question. By using narrow-spectrum antibiotics (when possible), the risk of selecting for antibiotic resistance in the commensal flora decreases. Selected Resources
Antibiotics are designed to fight bacteria by targeting specific parts of the bacteria’s structure or cellular machinery. However, over time, bacteria can defeat antibiotics in the following ways: Survival of the Fittest (Natural Selection)When bacteria are initially exposed to an antibiotic, those most susceptible to the antibiotic will die quickly, leaving any surviving bacteria to pass on their resistant features to succeeding generations. Biological MutationsSince bacteria are extremely numerous, random mutation of bacterial DNA generates a wide variety of genetic changes. Through mutation and selection, bacteria can develop defense mechanisms against antibiotics. For example, some bacteria have developed biochemical “pumps” that can remove an antibiotic before it reaches its target, while others have evolved to produce enzymes to inactivate the antibiotic. DNA ExchangeBacteria readily swap bits of DNA among both related and unrelated species. Thus, antibiotic-resistant genes from one type of bacteria may be incorporated into other bacteria. As a result, using any one antibiotic to treat a bacterial infection may result in other kinds of bacteria developing resistance to that specific antibiotic, as well as to other types of antibiotics. Rapid ReproductionBacteria reproduce rapidly, sometimes in as little as 20 minutes. Therefore, it does not take long for the antibiotic-resistant bacteria to comprise a large proportion of a bacterial population. Antibiotic-Resistant Bacteria and Effectiveness of Those DrugsTo date, all antibiotics have over time lost effectiveness against their targeted bacteria. The earliest antibiotics were developed in the 1940s. These "miracle drugs" held at bay such devastating diseases as pneumonia and tuberculosis, which had previously been untreatable. But the steady evolution of resistant bacteria has resulted in a situation in which, for some illnesses, doctors now have only one or two drugs “of last resort” to use against infections by superbugs resistant to all other drugs. For example: Staph AureusNearly all strains of Staphylococcus aureus in the United States are resistant to penicillin, and many are resistant to newer methicillin-related drugs. Since 1997, strains of S. aureus have been reported to have a decreased susceptibility to vancomycin, which has been the last remaining uniformly effective treatment. Campylobacter InfectionsToday, one out of six cases of Campylobacter infections, the most common cause of food borne illness, is resistant to fluoroquinolones (the drug of choice for treating food-borne illness). As recently as ten years ago, such resistance was negligible. Next StepsClearly, it is important to extend the useful lifetime of any drug that is effective against human disease. And today, this is even more important because few new antibiotics are being developed, and those that are developed tend to be extremely expensive. Historical Timeline of Antibiotics
Licensing & RegulationsContactMissouri Department of Health and Senior ServicesPO Box 570 Jefferson City, MO 65102-0570 Phone: 573-751-6113 or (toll-free) 866-628-9891 Fax: 573-526-0235 Email: |
