resistance
[re-zis´tans] 1. opposition, or counteracting force, as opposition of a conductor to passage of electricity or other energy or substance.
2. the natural ability of a normal organism to remain unaffected by noxious agents in its environment; see also
immunity.
3. in psychology or psychiatry, conscious or unconscious defenses against change, preventing repressed material from coming into awareness; they can take such forms as forgetfulness, evasions, embarrassment, mental blocks, denial, anger, superficial talk, intellectualization, or intensification of symptoms. It occurs because the blocked association or understanding would be too threatening to face at this point in the therapy; identification of what point the resistance comes at can be an important indicator of the patient's unconscious patterns.
airway resistance the opposition of the tissues of the air passages to air flow: the mouth-to-alveoli pressure difference divided by the rate of air flow. Symbol RA or RAW.
androgen resistance resistance of target organs to the action of
androgens, resulting in any of a spectrum of defects from a normal male phenotype in which men have normal genitalia but infertility to complete androgen resistance in which the individual has a female phenotype.
Complete androgen resistance is an extreme form of male
pseudohermaphroditism in which the individual is phenotypically female but is of XY chromosomal sex; there may be rudimentary uterus and tubes, but the gonads are typically testes, which may be abdominal or inguinal in position. Called also
testicular feminization and
testicular feminization syndrome.
Incomplete androgen resistance is any of various forms less than the complete type, manifested by a male phenotype with various degrees of ambiguous genitalia such as hypospadias and a small vaginal pouch, a hooded phallus, or a bifid scrotum that may or may not contain gonads.
drug resistance the ability of a microorganism to withstand the effects of a drug that are lethal to most members of its species.
multidrug resistance (
multiple drug resistance) a phenomenon seen in some malignant cell lines: cells that have developed natural resistance to a single cytotoxic compound are also resistant to structurally unrelated
chemotherapy agents. Called also
cross-resistance.
peripheral resistance resistance to the passage of blood through the small blood vessels, especially the arterioles.
vascular resistance the opposition to blood flow in a vascular bed; the pressure drop across the bed divided by the blood flow, conventionally expressed in peripheral resistance units. Symbol R or R.
drug re·sis·tance
the capacity of disease-causing microorganisms to withstand exposure to drugs previously toxic to them; acquired either through spontaneous mutation or by gradual selection of relatively resistant strains after drug exposure. Pathogenic microorganisms resist antibiotics by various mechanisms, including the production of enzymes (for example, β-lactamases) that chemically inactivate antibiotic molecules. In mixed infections of the respiratory tract, a β-lactamase (penicillinase) produced by one organism (for example, Haemophilus influenzae) can inactivate penicillin and so block its effectiveness against other organisms in the mixture that possess no resistance of their own (for example, group A β-hemolytic streptococci). Usually an organism that has acquired resistance to a given antibiotic is resistant to others in the same chemical class. Some bacteria transmit antibiotic resistance 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 resistance to certain antibiotics by acquiring plasmids from bacteria of another species.
Drug resistance is a growing problem worldwide. Many strains of bacteria, fungi, and parasites have developed resistance, 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 during the past decade. Resistance of gram-positive pathogens, including Streptococcus pneumoniae and group A β-hemolytic streptococci, to macrolide antibiotics has also increased rapidly. Widespread use of fluoroquinolones for respiratory and urinary tract infections has led to a steady decline in the susceptibility of aerobic gram-negative bacilli, particularly Pseudomonas aeruginosa, to these agents. Factors favoring development of drug resistance include inappropriate prescribing of antibiotics (for example, for viral infections); indiscriminate use of newly developed, extended-spectrum agents; irrational use of broad-spectrum antibiotics to treat β-hemolytic streptococcal infections; empiric prescribing of broad-spectrum agents for infections in certain populations (for example, children, the elderly, and residents of long-term care facilities); prescribing of sublethal and thus ineffective dosages; and failure of patients to complete courses of antibiotic treatment. Antimicrobial treatment that is begun empirically before results of cultures and sensitivity tests are available and does not include agents that are effective against resistant strains of organisms, increases morbidity and mortality. Infectious disease experts and public health authorities have called for restraint by primary care physicians in prescribing antibiotics, particularly in 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, because 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.
