Essay 111

Antibiotics are medications that are prescribed for people with bacterial infections. When you were a child and had an ear infection, your parents probably gave you spoonfuls of the pink medicine (Figure E11.1), and now when you have a sinus infection your doctor prescribes other antibiotics. These infections are easily treated and require fairly little inconvenience besides a trip to the doctor and pharmacy. Unfortunately, the days of easily treatable bacterial infections may soon be over because the bacteria that cause many diseases—including tuberculosis, malaria, ear infections, and gonorrhea—have become resistant to the antibiotics developed to cure them.

Antibiotic resistance arises as a result of natural selection. There is variation within any population of individuals, including within a population of bacterial cells. Some bacteria, even before exposure to the antibiotic, carry genes that enable them to resist it. You can develop a drug-resistant infection by selecting for the resistant bacteria within your own body or by contracting the resistant bacteria from someone else.

Tetracycline is an antibiotic used to kill the bacteria that cause acne. It works to prevent translation, the production of proteins, in prokaryotes. Since the workbenches of translation, the ribosomes, differ structurally in prokaryotes and eukaryotes, this antibiotic—like all effective antibiotics—selectively kills bacterial cells and not eukaryotic host cells. One bacterial cell in a population of millions may have a different DNA sequence in the region of DNA that encodes for a protein involved in translation. If this protein enables the bacterial cell to withstand tetracycline treatment, it will survive and pass on the resistant sequence to its offspring. In this manner, those bacteria that are not killed are selected for, and resistant infections develop.

The problem of resistance in bacteria seems to have originated from medical and agricultural overuse of antibiotics. Some patients ask their doctors to give them antibiotics for a cold, cough, or the flu—all of which are caused by viruses. For example, tetracycline would not be

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