Drug resistance is the 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
therapy. The number of drug-resistant bacterial strains has increased in part because of the
indiscriminate use of antibiotics, which have sometimes been over-prescribed. 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.
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 resistance to even the most powerful antibiotics has begun to appear.
Although drug companies are again concentrating on antibiotic research, no new products are expected in
the near future 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.
The mass production of antibiotics began during World War II with streptomycin and penicillin. Now most
antibiotics are produced by staged fermentations in which strains of microorganisms producing high yields
are grown under optimum conditions in nutrient media in fermentation tanks holding several thousand gallons.
The mold is strained out of the fermentation broth, and then the antibiotic is removed from the broth by
filtration, precipitation, and other separation methods. In some cases new antibiotics are laboratory synthesized,
while many antibiotics are produced by chemically modifying natural substances; many such derivatives are more
effective than the natural substances against infecting organisms or are better absorbed by the body, e.g., some
semisynthetic penicillins are effective against bacteria resistant to the parent substance.
|
