Survival of the Fittest
The increased prevalence of antibiotic resistance is an outcome of evolution. Any population of organisms,
bacteria included, naturally includes variants with unusual traits--in this case, the ability to withstand
an antibiotic's attack on a microbe. When a person takes an antibiotic, the drug kills the defenseless bacteria,
leaving behind--or "selecting," in biological terms--those that can resist it. These renegade bacteria then
multiply, increasing their numbers a millionfold in a day, becoming the predominant microorganism.
The antibiotic does not technically cause the resistance, but allows it to happen by creating a situation where
an already existing variant can flourish. "Whenever antibiotics are used, there is selective pressure for
resistance to occur. It builds upon itself. More and more organisms develop resistance to more and more drugs,"
says Joe Cranston, Ph.D., director of the department of drug policy and standards at the American Medical
Association in Chicago.
A patient can develop a drug-resistant infection either by contracting a resistant bug to begin with, or by having
a resistant microbe emerge in the body once antibiotic treatment begins. Drug-resistant infections increase risk
of death, and are often associated with prolonged hospital stays, and sometimes complications. These might
necessitate removing part of a ravaged lung, or replacing a damaged heart valve.
Bacterial Weaponry
Disease-causing microbes thwart antibiotics by interfering with their mechanism of action. For example,
penicillin kills bacteria by attaching to their cell walls, then destroying a key part of the wall. The wall
falls apart, and the bacterium dies. Resistant microbes, however, either alter their cell walls so penicillin
can't bind or produce enzymes that dismantle the antibiotic.
In another scenario, erythromycin attacks ribosomes, structures within a cell that enable it to make proteins.
Resistant bacteria have slightly altered ribosomes to which the drug cannot bind. The ribosomal route is also
how bacteria become resistant to the antibiotics tetracycline, streptomycin and gentamicin.
Antibiotic resistance...
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