Drug resistance
The resistance ( from the Latin resistentia for " resistance ") is the resistance of an organism against harmful environmental influences (such as parasites, infections, diseases, climate), with animal and plant pests ( bacteria ), also versus applied pesticides. Resistance may be hereditary, but also by environmental conditions (eg food ) to be generated. The creation of resistant breeds or varieties by mutation or crossover and continuous readout is one of the main objectives of the animal and plant breeding.
Biology (general)
Resistance of microorganisms
Populations of micro-organisms consist of thousands of individuals, some of which, for example, are less susceptible to an antibiotic than others. The use of an antibiotic, the most sensitive individuals die first, the most resistant to survive the longest. If the use of the antibiotic to fast you survive some of the most resistant individuals and multiply. The new population is on average more resistant than the old, because all current individuals from mother cells are derived, which were selected for low susceptibility to the antibiotic. Diseases that are caused by these pathogens that have already gone through this process several times, can hardly be treated with antibiotics.
Mechanisms of resistance are (1) efflux pumps, which are located in the outer membrane of the cells and, for example, to pump antibiotics out of the cells, so that the concentration inside the cell is at a critical level, (2) mutations in the gene coding for the protein coded, which represents the binding site / the site of action of the antibiotic in the exciter, and (3 ) metabolic detoxification, for example, by enzymes which cleave the active ingredient.
Sometimes can be activated by an antibiotic by an alternative pathway and survive as in antibiotic -containing environmental microorganisms in blocking a metabolic pathway.
Resistance can also be acquired by genes for antibiotic resistance encoded on plasmids, for example, be transferred from one bacterium to another by conjugation. There are mainly in hospitals pathogens (eg Pseudomonas ) which have acquired in this way several resistance factors, and are therefore become multi-resistant - a consequence of the continuous selection pressure by antibiotics necessary in about infectiological or intensive care departments.
Resistance of higher organisms
Just as many weeds to herbicides, insects to insecticides or fungicides against fungi are resistant today. This has consequences for the modern agriculture, but also in the fight against spread of insect-borne diseases ( eg malaria ).
Resistance of plants
In plants, resistance to pests and diseases is referred to as resistance, while the resistance to abiotic factors (for example, cold, herbicides) is referred to as tolerance. Resistance responses of plants to pests and diseases are classified based on the mechanisms of action in different types.
In non-host resistance all varieties and genotypes of a plant species are resistant to all races of a pathogen.
If there is now the fundamental ability of a pathogen, disease in a plant species trigger (eg the pathogen Phytophthora infestans triggers the late blight on tomato and potato from ), so individual host genotypes to certain strains or races of the pathogen may be resistant. This resistance is so racially specific and characterized by a qualitative interaction (yes - no). Virulent races run on susceptible plants to unhindered infestation at the races avirulent infection in plants is completely stopped with the right resistance. Race -specific resistance are usually based on only one or a very few genes. Such complete resistance are also called vertical resistance, since their more or less monogenic inheritance is clearly reflected in the offspring. The mechanism of qualitative resistance is often the hypersensitive cell death. That is, once a plant cell with an avirulent race comes into contact, the cell dies and may the neighboring cells from before the pathogen is able to penetrate to the next cell, and thus kills the pathogen. The qualitative resistance can be overcome quickly by many pathogen.
In contrast to race-specific resistance, there is also partial resistance, the infestation to admit though, but slow down the infection process dramatically. Such gradual resistance responses (horizontal resistance) based on a variety polygenic controlled resistance mechanisms that are largely independent of the triggered Pathogenrassen. Therefore, they are ( fewer / more ) referred to as non-specific or race- quantitatively. Basically, it is much more difficult for pathogens to adapt to these complex quantitative resistance, as to their circumvention several compensatory mutations must occur simultaneously, which significantly rarer statistically. By crossing several partial resistances are combined, which can also lead to complete resistance. Partial resistance are usually found in only slightly affected plants.
Both the qualitative and quantitative resistance reactions are based on biochemical processes in the plant, which, once they have been triggered often are active for a certain time and thus the plant against subsequent infections temporarily protect analogous to a very short-term vaccination ( typical action time three to seven days ). This process is known as induced resistance.
In plants has been observed to react at an increased amount of sulfur in the environment with sulfur - induced resistance.
Resistance in humans and animals
In humans and animals, there are in addition to individual resistance mechanisms yet another resistance, it will be acquired by an organism during its lifetime against pathogens, the so-called immunity. The process of generating an immunity is also called immunization, and consists in an adaptation of the immune system to the pathogen, which was exposed to the organism. Against changing temperature influences, there is also a temperature resistance.
Pharmacology
In pharmacology and related disciplines resistance refers to the fact that usually do not work -related influences, for example, when a neurotransmitter or a hormone no longer acts as usual, because the lack receptors on the target cells or are blocked. In order to achieve the same intensity of effect, dose escalation is then necessary for the effective dose increases. A well-known example is insulin resistance. In the radiochemistry possible resistance to low doses of radiation is discussed as a result of hormesis, which probably arise from a threshold of radiation dose due to the activation of repair mechanisms of the cell.
Neurobiology
In neurobiology resistance to re stimuli is called habituation.