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drug resistance

drug resistance, condition in which infecting bacteria can resist the destructive effects of drugs such as antibiotics and sulfa drugs. 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 mutations 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 malaria and tuberculosis. 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, no new products are expected until the turn of the century, and many infectious-disease experts are urging that doctors consider the public health risk before prescribing antibiotics and that the government regulate the use of antibiotics in agriculture.

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

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

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