- Opposition to something, or the ability to withstand it. For example, some forms of staphylococcus are resistant to treatment with antibiotics.
* * *1. A force exerted in opposition to an active force. 2. The opposition in a conductor to the passage of a current of electricity, whereby there is a loss of energy and a production of heat; specifically, the potential difference in volts across the conductor per ampere of current flow; unit : ohm. Cf.:impedance (1). 3. The opposition to flow of a fluid through one or more passageways ( e.g., blood flow, respiratory gases in the tracheobronchial tree), analogous to (2); units are usually those of pressure difference per unit flow. Cf.:impedance (2). 4. In psychoanalysis, an individual's unconscious defense against bringing repressed thoughts to consciousness. 5. The ability of red blood cells to resist hemolysis and to preserve their shape under varying degrees of osmotic pressure in the blood plasma. 6. The natural or acquired ability of an organism to maintain its immunity to or to resist the effects of an antagonistic agent, e.g., pathogenic microorganism, toxin, drug. [L. re-sisto, to stand back, withstand]- airway r. in physiology, the r. to flow of gases during ventilation due to obstruction or turbulent flow in the upper and lower airways; to be differentiated during inhalation from r. to inflation due to decreases in pulmonary or thoracic compliance.- bacteriophage r. r. of a bacterial mutant to infection by a bacteriophage to which the parent (wild-type) strain is susceptible.- dicumarol r. [MIM*122700] an autosomal dominant disorder characterized by r. to dicumarol, over and above general variability in tolerance to the drug; caused by mutation in the coumarin 7-hydroxylase gene (CYP2A6) on chromosome 19p.- drug r. the capacity of disease-causing microorganisms to withstand drugs previously toxic to them; achieved by spontaneous mutation or through selective pressure after exposure to the drug in question. Pathogenic microorganisms resist antibiotics by various mechanisms, including the production of enzymes ( e.g., β-lactamases) that chemically inactivate antibiotic molecules. In mixed infections of the respiratory tract, a β-lactamase (penicillinase) produced by one organism ( e.g., Haemophilus influenzae) can inactivate penicillin and so block its effectiveness against other organisms in the mixture that possess no r. of their own ( e.g., group A β-hemolytic streptococci). Usually an organism that has acquired r. to a given antibiotic is resistant to others in the same chemical class. Some bacteria transmit antibiotic r. to their offspring not chromosomally but via plasmids, which lie outside the bacterial nucleus but perform certain genetic functions. Bacteria of one species can develop r. to certain antibiotics by acquiring plasmids from bacteria of another species.Drug r. is a growing problem worldwide. Many strains of bacteria, fungi, and parasites have developed r., including pneumococci, gonococci, salmonellae, Mycobacterium tuberculosis, Tinea tonsurans, and Plasmodium falciparum. In some parts of the U.S., 40% of pneumococcal isolates and 90% of staphylococci are resistant to penicillin. The prevalence of both vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus has increased 20-fold since 1989. Factors favoring development of antibiotic r. include inappropriate prescribing of antibiotics (e.g., to treat viral infections); indiscriminate use of newly developed, extended-spectrum agents; empiric and broad-spectrum treatment of infections in certain populations (e.g., children, the elderly, and residents of long-term care facilities); prescribing of sublethal doses; and failure of patients to complete courses of antibiotic treatment. The Centers for Disease Control and Prevention estimates that U.S. physicians write 50 million unnecessary antibiotic prescriptions annually, including 17 million to treat the common cold. Infectious disease experts and public health authorities have called for restraint by primary care physicians in prescribing antibiotics, particularly for children and for uncomplicated upper respiratory infections, acute bronchitis (nearly always viral), and acute sinusitis and otitis media (in neither of which have reliable diagnostic criteria for bacterial infection been established). They have also stressed the importance of public education, since inappropriate expectations of patients or their parents have been a driving factor in antibiotic overuse by physicians. Administration of antibiotics to livestock animals, chiefly for disease prophylaxis and growth promotion, has also contributed to the emergence of resistant strains of bacteria.- expiratory r. r. to flow of gas out of the lungs or the total r. to flow of gas during the expiratory phase of the respiratory cycle.- impact r. the ability of a lens for eyewear to withstand impact without shattering or breaking, i.e., of a 38-inch steel ball dropped 50 ft; criteria for determination of impact r. are specified by U.S. regulations.- inductive r. SYN: reactance.- insulin r. diminished effectiveness of insulin in lowering plasma glucose levels, arbitrarily defined as a daily requirement of at least 200 units of insulin to prevent hyperglycemia or ketosis; usually due to binding of insulin or insulin receptor sites by antibodies; associated with obesity, ketoacidosis, and infection.Impairment of the normal response of muscle and other cells to endogenous or exogenous insulin often complicates the deficiency of endogenous insulin that is characteristic of type 2 diabetes mellitus. It is a peripheral phenomenon and can occur even when the quality and quantity of insulin produced by the pancreas are normal. It apparently results from a decrease in the number of insulin receptor sites on cells, a malfunction of the biochemical glucose transport system, or both. Insulin r. is often associated with high levels of circulating antibody to insulin receptors. The phenomenon of insulin r. explains why some people with type 2 diabetes have hyperinsulinemia in the fasting state, often coexisting with elevated plasma glucose levels. Insulin r. correlates closely with obesity in diabetes. It occurs less frequently in lean diabetics, whose principal problem is usually primary failure of insulin production. Insulin r. is often seen in persons with or without frank diabetes who have other endocrine or systemic disorders, including dyslipidemias, hypertension, hyperuricemia, and chronic infection. Some women with polycystic ovaries, hirsutism, and anovulation also have insulin r. and hyperinsulinemia. Troglitazone, a newer agent used in the treatment of type 2 diabetes mellitus, improves insulin sensitivity.- multidrug r. the insensitivity of various tumors to a variety of chemically related anticancer drugs; mediated by a process of inactivating the drug or removing it from the target tumor cells.- mutual r. SYN: antagonism.- systemic vascular r. an index of arteriolar compliance or constriction throughout the body; proportional to the blood pressure divided by the cardiac output.- thyrotropin r. an autosomal recessive disorder in which the thyrocytes are unresponsive to thyrotropin. Cf.:pseudohypoparathyroidism.- total peripheral r. (TPR) the total r. to flow of blood in the systemic circuit; the quotient produced by dividing the mean arterial pressure by the cardiac minute-volume. SYN: peripheral r..
* * *1 a) power or capacity to resist esp the inherent ability of an organism to resist harmful influences (as disease, toxic agents, or infection)b) the capacity of a species or strain of microorganism to survive exposure to a toxic agent (as a drug) formerly effective against it due to genetic mutation and selection for and accumulation of genes conferring protection from the agent esp. as a result of overuse of the agent which selectively destroys individual microorganisms lacking the protective genes2 a) the opposition offered by a body to the passage through it of a steady electric currentb) opposition or impediment to the flow of a fluid (as blood or respiratory gases) through one or more passages see vascular resistance3) a psychological defense mechanism wherein a psychoanalysis patient rejects, denies, or otherwise opposes therapeutic efforts by the analyst
* * *n.1. the degree of immunity that the body possesses: a measure of its ability to withstand disease.2. the degree to which a disease or disease-causing organism remains unaffected by antibiotics or other drugs.
* * *re·sis·tance (re-zisґtəns) [L. resistere to stand back] 1. opposition, or counteracting force. 2. the natural ability of an organism to resist microorganisms or toxins produced in disease. 3. the opposition to the flow of electrical current between two points of a circuit; it is the voltage drop between the two points divided by the current flow, in SI units expressed in ohms. Symbol R or R>. 4. in psychiatry, conscious or unconscious defenses that prevent material in the unconscious, as repressed thoughts, from coming into awareness.
Medical dictionary. 2011.