drug resistance

drug resistance,

condition in which infecting bacteriabacteria
[pl. of bacterium], microscopic unicellular prokaryotic organisms characterized by the lack of a membrane-bound nucleus and membrane-bound organelles. Once considered a part of the plant kingdom, bacteria were eventually placed in a separate kingdom, Monera.
..... Click the link for more information. can resist the destructive effects of drugs such as antibioticsantibiotic,
any of a variety of substances, usually obtained from microorganisms, that inhibit the growth of or destroy certain other microorganisms. Types of Antibiotics
..... Click the link for more information. and sulfa drugssulfa drug,
any of a class of synthetic chemical substances derived from sulfanilamide, or para-aminobenzenesulfonamide. Sulfa drugs are used to treat bacterial infections, although they have largely been replaced for this purpose by antibiotics; some are also used in the
..... Click the link for more information. . Drug resistance has become a serious public health problem, since many disease-causing bacteria are no longer susceptible to previously effective drug therapies. For nearly 50 years after the first antibiotic, penicillin, became available in the 1940s, people took antibiotics' effectiveness against bacterial infections for granted. By the 1960s some doctors were predicting the end of infectious diseases. By the 1990s, however, a "post-antibiotic era," characterized by the proliferation of untreatable bacterial strains, was considered inevitable, and the rate at which bacteria were becoming resistant to antibiotics was catching up with the rate at which new antibiotics were being produced.

The number of drug-resistant bacterial strains has increased in part because of the indiscriminate use of antibiotics, which have sometimes been overprescribed. Such misuse speeds the process by destroying bacteria that would compete with resistant strains. In addition, patients sometimes stop treatment when they start to feel better, leaving a residual population of bacteria that is likely to be more resistant to drug treatment. Another source of resistance is the routine use of antibiotics in animal feed to enhance growth, a practice that has led to resistant strains of Escherichia coli and Salmonella that have been passed on to consumers. The presence of drugs in the water supply, due at least in part to human and animal excretion and the disposal of unused drugs, is also believed to contribute to drug resistance in bacteria.

Resistance is due to random genetic mutationsmutation,
in biology, a sudden, random change in a gene, or unit of hereditary material, that can alter an inheritable characteristic. Most mutations are not beneficial, since any change in the delicate balance of an organism having a high level of adaptation to its environment
..... Click the link for more information. in the bacterial cell that alter its sensitivity to a single drug or to chemically similar drugs through a variety of mechanisms. Many bacteria can transfer their resistance to other bacteria of the same or different species. Resistance has occurred in common infectious bacteria such as pneumococcus (a cause of pneumonia, meningitis, and childhood ear infections) and enterococcus (a cause of wound infections). It has also occurred in such diseases as malariamalaria,
infectious parasitic disease that can be either acute or chronic and is frequently recurrent. Malaria is common in Africa, Central and South America, the Mediterranean countries, Asia, and many of the Pacific islands.
..... Click the link for more information. , tuberculosistuberculosis
(TB), contagious, wasting disease caused by any of several mycobacteria. The most common form of the disease is tuberculosis of the lungs (pulmonary consumption, or phthisis), but the intestines, bones and joints, the skin, and the genitourinary, lymphatic, and
..... Click the link for more information. , and gonorrheagonorrhea
, common infectious disease caused by a bacterium (Neisseria gonorrhoeae), involving chiefly the mucous membranes of the genitourinary tract. It may occasionally spread to membranes in other parts of the body, especially those of the joints and the eyes.
..... Click the link for more information. . Concerns are increasing as strains develop resistance to multiple drugs, including even the most powerful antibiotics (e.g., vancomycin). Although drug companies are again concentrating on antibiotic research, seeking new antibiotics and attempting to develop chemically altered derivatives of existing ones that can block bacterial resistance, such research does not necessarily proceed swiftly and the testing required to ensure drug safety also slows the introduction of new antibiotics. Many infectious-disease experts have urged that doctors consider the public health risk before prescribing antibiotics and that the government regulate the use of antibiotics in agriculture. Beginning in 2017, the Food and Drug Administration ended over-the-counter agricultural use of antimicrobial drugs deemed medically important; it also has moved to phase out voluntarily the use of such drugs for enhancing livestock growth.

Bibliography

See S. Levy, The Antibiotic Paradox (1992).

Drug resistance

The ability of an organism to resist the action of an inhibitory molecule or compound. Examples of drug resistance include disease-causing bacteria evading the activity of antibiotics, the human immunodeficiency virus resisting antiviral agents, and human cancer cells replicating despite the presence of chemotherapy agents. There are many ways in which cells or organisms become resistant to drugs, and some organisms have developed many resistance mechanisms, each specific to a different drug. Drug resistance is best understood as it applies to bacteria, and the increasing resistance of many common disease-causing bacteria to antibiotics is a global crisis.

Genetic basis

Some organisms or cells are innately or inherently resistant to the action of specific drugs. In other cases, the development of drug resistance involves a change in the genetic makeup of the organism. This change can be either a mutation in a chromosomal gene or the acquisition of new genetic material from another cell or the environment.

Organisms may acquire deoxyribonucleic acid (DNA) that codes for drug resistance by a number of mechanisms. Transformation involves the uptake of DNA from the environment. Once DNA is taken up into the bacterial cell, it can recombine with the recipient organism's chromosomal DNA. This process plays a role in the development and spread of antibiotic resistance, which can occur both within and between species.

Transduction, another mechanism by which new DNA is acquired by bacteria, is mediated by viruses that infect bacteria (bacteriophages). Bacteriophages can integrate their DNA into the bacterial chromosome.

Conjugation is the most common mechanism of acquisition and spread of resistance genes among bacteria. This process, which requires cell-to-cell contact, involves direct transfer of DNA from the donor cell to a recipient cell. While conjugation can involve cell-to-cell transfer of chromosomal genes, bacterial resistance genes are more commonly transferred on nonchromosomal genetic elements known as plasmids or transposons. See Deoxyribonucleic acid (DNA)

Mechanisms of resistance

The four most important antibiotic resistance mechanisms are alteration of the target site of the antibiotic, enzyme inactivation of the antibiotic, active transport of the antibiotic out of the bacterial cell, and decreased permeability of the bacterial cell wall to the antibiotic (see illustration).

Four common mechanisms of antibiotics resistance

By altering the target site to which an antibiotic must bind, an organism may decrease or eliminate the activity of the antibiotic. Alteration of the target site is the mechanism for one of the most problematic antibiotic resistances worldwide, methicillin resistance among Staphylococcus aureus. See Bacterial genetics

The most common mechanism by which bacteria are resistant to antibiotics is by producing enzymes that inactivate the drugs. For example, β-lactam antibiotics (penicillins and cephalosporins) can be inactivated by enzymes known as β-lactamases.

Active transport systems (efflux pumps) have been described for the removal of some antibiotics (such as tetracyclines, macrolides, and quinolones) from bacterial cells. In these situations, even though the drug can enter the bacterial cell, active efflux of the agent prevents it from accumulating and interfering with bacterial metabolism or replication.

Bacteria are intrinsically resistant to many drugs based solely on the fact that the drugs cannot penetrate the bacterial cell wall or cell membrane. In addition, bacteria can acquire resistance to a drug by an alteration in the porin proteins that form channels in the cell membrane. The resistance that Pseudomonas aeruginosa exhibits to a variety of penicillins and cephalosporins is mediated by an alteration in porin proteins.

Promoters

In the hospital environment, many factors combine to promote the development of drug resistance among bacteria. Increasing use of powerful new antibiotics gives selective advantage to the most resistant bacteria. In addition, advances in medical technology allow for the survival of sicker patients who undergo frequent invasive procedures. Finally, poor infection control practices in hospitals allow for the unchecked spread of already resistant strains of bacteria.

Outside the hospital environment, other important factors promote antibiotic resistance. The overuse of antibiotics in outpatient medicine and the use of antibiotics in agriculture exert selective pressure for the emergence of resistant bacterial strains. The spread of these resistant strains is facilitated by increasing numbers of children in close contact at day care centers, and by more national and international travel.

Control

A multifaceted worldwide effort will be required to control drug resistance among disease-causing microorganisms. Ongoing programs to decrease the use of antibiotics, both in the clinics and in agriculture, will be necessary. The increased use of vaccines to prevent infection can help limit the need for antibiotics. Finally, the development of novel classes of antibiotics to fight emerging resistant bacteria will be required. See Antibiotic, Bacteria

drug resistance

[¦drəg ri′zis·təns] (microbiology) A decreased reactivity of living organisms to the injurious actions of certain drugs and chemicals.

drug resistance

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 R_A or R_AW.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" >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.insulin resistance see insulin resistance.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.pulmonary vascular resistance the resistance" >vascular resistance of the pulmonary circulation; the difference between the mean pulmonary arterial pressure and the left atrial filling pressure divided by the cardiac output. Called also total pulmonary vascular resistance.total peripheral resistance the resistance" >vascular resistance of the systemic circulation: the difference between the mean pressure" >arterial pressure and central venous pressure divided by the output" >cardiac output.total pulmonary resistance (total pulmonary vascular resistance) pulmonary vascular resistance.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.

drug resistance

The ability of bacteria and other microorganisms to withstand a drug to which they were once sensitive

drug re·sis·tance

(drŭg rĕ-zis'tăns) The capacity of disease-causing pathogens to withstand drugs previously toxic to them; achieved by spontaneous mutation or through selective pressure after exposure to the drug in question.

drug re·sis·tance

(drŭg rĕ-zis'tăns) Capacity of disease-causing microorganisms to withstand exposure to drugs previously toxic to them.

单词	drug resistance
释义	DictionarySeedrug drug resistance drug resistance, condition in which infecting bacteriabacteria [pl. of bacterium], microscopic unicellular prokaryotic organisms characterized by the lack of a membrane-bound nucleus and membrane-bound organelles. Once considered a part of the plant kingdom, bacteria were eventually placed in a separate kingdom, Monera. ..... Click the link for more information. can resist the destructive effects of drugs such as antibioticsantibiotic, any of a variety of substances, usually obtained from microorganisms, that inhibit the growth of or destroy certain other microorganisms. Types of Antibiotics ..... Click the link for more information. and sulfa drugssulfa drug, any of a class of synthetic chemical substances derived from sulfanilamide, or para-aminobenzenesulfonamide. Sulfa drugs are used to treat bacterial infections, although they have largely been replaced for this purpose by antibiotics; some are also used in the ..... Click the link for more information. . Drug resistance has become a serious public health problem, since many disease-causing bacteria are no longer susceptible to previously effective drug therapies. For nearly 50 years after the first antibiotic, penicillin, became available in the 1940s, people took antibiotics' effectiveness against bacterial infections for granted. By the 1960s some doctors were predicting the end of infectious diseases. By the 1990s, however, a "post-antibiotic era," characterized by the proliferation of untreatable bacterial strains, was considered inevitable, and the rate at which bacteria were becoming resistant to antibiotics was catching up with the rate at which new antibiotics were being produced. The number of drug-resistant bacterial strains has increased in part because of the indiscriminate use of antibiotics, which have sometimes been overprescribed. Such misuse speeds the process by destroying bacteria that would compete with resistant strains. In addition, patients sometimes stop treatment when they start to feel better, leaving a residual population of bacteria that is likely to be more resistant to drug treatment. Another source of resistance is the routine use of antibiotics in animal feed to enhance growth, a practice that has led to resistant strains of Escherichia coli and Salmonella that have been passed on to consumers. The presence of drugs in the water supply, due at least in part to human and animal excretion and the disposal of unused drugs, is also believed to contribute to drug resistance in bacteria. Resistance is due to random genetic mutationsmutation, in biology, a sudden, random change in a gene, or unit of hereditary material, that can alter an inheritable characteristic. Most mutations are not beneficial, since any change in the delicate balance of an organism having a high level of adaptation to its environment ..... Click the link for more information. in the bacterial cell that alter its sensitivity to a single drug or to chemically similar drugs through a variety of mechanisms. Many bacteria can transfer their resistance to other bacteria of the same or different species. Resistance has occurred in common infectious bacteria such as pneumococcus (a cause of pneumonia, meningitis, and childhood ear infections) and enterococcus (a cause of wound infections). It has also occurred in such diseases as malariamalaria, infectious parasitic disease that can be either acute or chronic and is frequently recurrent. Malaria is common in Africa, Central and South America, the Mediterranean countries, Asia, and many of the Pacific islands. ..... Click the link for more information. , tuberculosistuberculosis (TB), contagious, wasting disease caused by any of several mycobacteria. The most common form of the disease is tuberculosis of the lungs (pulmonary consumption, or phthisis), but the intestines, bones and joints, the skin, and the genitourinary, lymphatic, and ..... Click the link for more information. , and gonorrheagonorrhea , common infectious disease caused by a bacterium (Neisseria gonorrhoeae), involving chiefly the mucous membranes of the genitourinary tract. It may occasionally spread to membranes in other parts of the body, especially those of the joints and the eyes. ..... Click the link for more information. . Concerns are increasing as strains develop resistance to multiple drugs, including even the most powerful antibiotics (e.g., vancomycin). Although drug companies are again concentrating on antibiotic research, seeking new antibiotics and attempting to develop chemically altered derivatives of existing ones that can block bacterial resistance, such research does not necessarily proceed swiftly and the testing required to ensure drug safety also slows the introduction of new antibiotics. Many infectious-disease experts have urged that doctors consider the public health risk before prescribing antibiotics and that the government regulate the use of antibiotics in agriculture. Beginning in 2017, the Food and Drug Administration ended over-the-counter agricultural use of antimicrobial drugs deemed medically important; it also has moved to phase out voluntarily the use of such drugs for enhancing livestock growth. Bibliography See S. Levy, The Antibiotic Paradox (1992). Drug resistance The ability of an organism to resist the action of an inhibitory molecule or compound. Examples of drug resistance include disease-causing bacteria evading the activity of antibiotics, the human immunodeficiency virus resisting antiviral agents, and human cancer cells replicating despite the presence of chemotherapy agents. There are many ways in which cells or organisms become resistant to drugs, and some organisms have developed many resistance mechanisms, each specific to a different drug. Drug resistance is best understood as it applies to bacteria, and the increasing resistance of many common disease-causing bacteria to antibiotics is a global crisis. Genetic basis Some organisms or cells are innately or inherently resistant to the action of specific drugs. In other cases, the development of drug resistance involves a change in the genetic makeup of the organism. This change can be either a mutation in a chromosomal gene or the acquisition of new genetic material from another cell or the environment. Organisms may acquire deoxyribonucleic acid (DNA) that codes for drug resistance by a number of mechanisms. Transformation involves the uptake of DNA from the environment. Once DNA is taken up into the bacterial cell, it can recombine with the recipient organism's chromosomal DNA. This process plays a role in the development and spread of antibiotic resistance, which can occur both within and between species. Transduction, another mechanism by which new DNA is acquired by bacteria, is mediated by viruses that infect bacteria (bacteriophages). Bacteriophages can integrate their DNA into the bacterial chromosome. Conjugation is the most common mechanism of acquisition and spread of resistance genes among bacteria. This process, which requires cell-to-cell contact, involves direct transfer of DNA from the donor cell to a recipient cell. While conjugation can involve cell-to-cell transfer of chromosomal genes, bacterial resistance genes are more commonly transferred on nonchromosomal genetic elements known as plasmids or transposons. See Deoxyribonucleic acid (DNA) Mechanisms of resistance The four most important antibiotic resistance mechanisms are alteration of the target site of the antibiotic, enzyme inactivation of the antibiotic, active transport of the antibiotic out of the bacterial cell, and decreased permeability of the bacterial cell wall to the antibiotic (see illustration). Four common mechanisms of antibiotics resistance By altering the target site to which an antibiotic must bind, an organism may decrease or eliminate the activity of the antibiotic. Alteration of the target site is the mechanism for one of the most problematic antibiotic resistances worldwide, methicillin resistance among Staphylococcus aureus. See Bacterial genetics The most common mechanism by which bacteria are resistant to antibiotics is by producing enzymes that inactivate the drugs. For example, β-lactam antibiotics (penicillins and cephalosporins) can be inactivated by enzymes known as β-lactamases. Active transport systems (efflux pumps) have been described for the removal of some antibiotics (such as tetracyclines, macrolides, and quinolones) from bacterial cells. In these situations, even though the drug can enter the bacterial cell, active efflux of the agent prevents it from accumulating and interfering with bacterial metabolism or replication. Bacteria are intrinsically resistant to many drugs based solely on the fact that the drugs cannot penetrate the bacterial cell wall or cell membrane. In addition, bacteria can acquire resistance to a drug by an alteration in the porin proteins that form channels in the cell membrane. The resistance that Pseudomonas aeruginosa exhibits to a variety of penicillins and cephalosporins is mediated by an alteration in porin proteins. Promoters In the hospital environment, many factors combine to promote the development of drug resistance among bacteria. Increasing use of powerful new antibiotics gives selective advantage to the most resistant bacteria. In addition, advances in medical technology allow for the survival of sicker patients who undergo frequent invasive procedures. Finally, poor infection control practices in hospitals allow for the unchecked spread of already resistant strains of bacteria. Outside the hospital environment, other important factors promote antibiotic resistance. The overuse of antibiotics in outpatient medicine and the use of antibiotics in agriculture exert selective pressure for the emergence of resistant bacterial strains. The spread of these resistant strains is facilitated by increasing numbers of children in close contact at day care centers, and by more national and international travel. Control A multifaceted worldwide effort will be required to control drug resistance among disease-causing microorganisms. Ongoing programs to decrease the use of antibiotics, both in the clinics and in agriculture, will be necessary. The increased use of vaccines to prevent infection can help limit the need for antibiotics. Finally, the development of novel classes of antibiotics to fight emerging resistant bacteria will be required. See Antibiotic, Bacteria drug resistance [¦drəg ri′zis·təns] (microbiology) A decreased reactivity of living organisms to the injurious actions of certain drugs and chemicals. drug resistance 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 R_A or R_AW.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" >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.insulin resistance see insulin resistance.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.pulmonary vascular resistance the resistance" >vascular resistance of the pulmonary circulation; the difference between the mean pulmonary arterial pressure and the left atrial filling pressure divided by the cardiac output. Called also total pulmonary vascular resistance.total peripheral resistance the resistance" >vascular resistance of the systemic circulation: the difference between the mean pressure" >arterial pressure and central venous pressure divided by the output" >cardiac output.total pulmonary resistance (total pulmonary vascular resistance) pulmonary vascular resistance.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. drug resistance The ability of bacteria and other microorganisms to withstand a drug to which they were once sensitive drug re·sis·tance (drŭg rĕ-zis'tăns) The capacity of disease-causing pathogens to withstand drugs previously toxic to them; achieved by spontaneous mutation or through selective pressure after exposure to the drug in question. drug re·sis·tance (drŭg rĕ-zis'tăns) Capacity of disease-causing microorganisms to withstand exposure to drugs previously toxic to them. FinancialSeeResistanceThesaurusSeeresistance
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