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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: Resistance DefinitionResistance may be defined as ‘a heritable change in the sensitivity of a pest population that is reflected in the repeated failure of a product to achieve the expected level of control when used according to the label recommendation for that pest species’. Cross-resistance occurs when resistance to one insecticide confers resistance to another insecticide, even where the insect has not been exposed to the latter product. Clearly, because pest insect populations are usually large in size and they breed quickly, there is always a risk that insecticide resistance may evolve, especially when insecticides are misused or over-used. BackgroundFollowing the introduction of synthetic organic insecticides in the 1940’s, such as DDT, it was not long before the first cases of resistance were detected and by 1947, resistance to DDT was confirmed in houseflies. Thereafter, with every new insecticide introduction, cyclodienes, organophosphates, carbamates, formamidines, pyrethroids, Bacillus thuringiensis, spinosyns andneonicotinoids, cases of resistance appeared some 2 to 20 years after their introduction in a number of key pest species. This phenomenon has been described as the ‘pesticide treadmill’, and the sequence is familiar. As a result of continued applications over time the pest evolves resistance to the insecticide and the resistant strain becomes increasingly difficult to control at the labeled rate and frequency. This in turn has often led to more frequent applications of the insecticide. The intensity of the resistance and the frequency of insecticide-resistant individuals in the population both increase still further and problems of control continue to worsen as yet more product is applied. Eventually users switch to another pesticide if one is available. The genetics of the heritable resistance traits and the intensive repeated application of pesticides, together are responsible for the rapid build-up of resistance in most insects and mites. DevelopmentNatural selection by an insecticide allows some initially very rare, naturally occurring, pre-adapted insects with resistance genes to survive and pass the resistance trait on to their offspring. Through continued application of insecticides with the same MoA, selection for the resistant individuals continues so the proportion of resistant insects in the population increases, while susceptible individuals are eliminated by the insecticide. Under permanent selection pressure, resistant insects outnumber susceptible ones and the insecticide is no longer effective. The speed with which resistance develops depends on several factors, including how fast the insects reproduce, the migration and host range of the pest, the availability of nearby susceptible populations, the persistence and specificity of the crop protection product, and the rate, timing and number of applications made. Resistance increases fastest in situations such as greenhouses, where insects or mites reproduce quickly, there is little or no immigration of susceptible individuals and the user may spray frequently. See further information on insecticide resistance and IRM as developed by the University of Nebraska. What is natural selection how can natural selection be detected in populations of organisms?Natural selection is the process through which populations of living organisms adapt and change. Individuals in a population are naturally variable, meaning that they are all different in some ways. This variation means that some individuals have traits better suited to the environment than others.
What are 4 examples of natural selection?Deer Mouse.. Warrior Ants. ... . Peacocks. ... . Galapagos Finches. ... . Pesticide-resistant Insects. ... . Rat Snake. All rat snakes have similar diets, are excellent climbers and kill by constriction. ... . Peppered Moth. Many times a species is forced to make changes as a direct result of human progress. ... . 10 Examples of Natural Selection. « previous. ... . What are the 5 steps of natural selection?Natural selection is a simple mechanism that causes populations of living things to change over time. In fact, it is so simple that it can be broken down into five basic steps, abbreviated here as VISTA: Variation, Inheritance, Selection, Time and Adaptation.
What are the 4 steps of evolution by natural selection?There are four principles at work in evolution—variation, inheritance, selection and time. These are considered the components of the evolutionary mechanism of natural selection.
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