Antibiotic resistance can be detected by measuring the zone of inhibition, in which bacteria will not grow near the antibiotic on a culture plate. The overuse of antibiotics has resulted from the tendency of doctors to prescribe antibiotics for mild bacterial infections, and for viral infections that cannot be controlled by antibiotics. This evolution can occur very rapidly. Consider these examples:

- Intestinal infections. A study of Swiss hospitals showed that between 1983 and 1990, when only 1.4 percent of the patients were receiving routine antibiotic administrations, there were no samples of the bacterium E. coli that could resist any of the five kinds of fluoroquinolone antibiotics. (E. coli is a bacterium that lives in human intestines and is usually harmless, but it can cause infections in people with impaired immune systems.) However, between 1991 and 1993, during which time 45 percent of the patients were receiving routine antibiotic administrations, 28 percent of the E. coli samples were resistant to all five of the antibiotics.

- Sexually transmitted diseases (STDs). From 1993 to 2001 Hawaii experienced a rapid increase in the incidence of gonorrhea bacteria (Neisseria gonorrhoeae) that resist fluoroquinolones. Gonorrhea had originally been treated with penicillin, but when the bacteria evolved resistance to penicillin, doctors substituted tetracycline, which also became ineffective and was replaced by fluoroquinolines, which are now becoming ineffective also.

- Food poisoning. Forty percent of the samples of the food poisoning bacteria of the genus Campylobacter in Finland could resist fluoroquinolones in 1996, but 60 percent were resistant in 1999. In America antibiotic-resistant Salmonella was present in only 5 percent of samples in 1997 but in 10 percent of samples in 2001.

- Spinal infections. In 1996, 10.4 percent of samples of the meningitis bacterium Streptococcus pneumoniae resisted penicillin, but by 2001, 51.5 percent of the samples were resistant to penicillin; resistance to macrolide antibiotics increased from 16.5 percent to 30.0 percent during that time.

- General infections. Over 90 percent of the strains of "staph" (Staphylococcus aureus), a common cause of infections, now resist penicillin and related antibiotics.

Another reason that antibiotic resistance can spread rapidly through bacterial populations is that bacteria can transfer pieces of DNA from one to another, and this transfer can occur even from one bacterial species to another. In eukaryotic species that are totally separate, resistance cannot evolve until the resistance mutations occur within their separate populations; but in bacteria, one resistant species can donate resistant genes to another species! . . .

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