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Modern medicine has engaged disease-causing microbes in an escalating arms race, so that as soon as drug developers launch a new weapon--an antibiotic, for example--their microbial foes respond by shoring up their own defenses. Sometimes bacteria and parasites undergo random mutations that spontaneously confer resistance. More frequently, they acquire survival-enhancing characteristics in the process of exchanging DNA with other microbes that have already developed resistance.
Bacteria and parasites do not do this on purpose, of course, but the effect is much the same. In 1944, for example, penicillin appeared to be a magic bullet against staphylococcal infections. The problem was, it failed to kill every single bug, and those that survived the onslaught slowly began to multiply. The result: by the 1950s most staph infections had become highly resistant to penicillin. The same fate met penicillin's successors, erythromycin and methicillin; now it appears to be vancomycin's turn.
For this reason, it is not enough to come up with new drugs; it is also imperative for us to try our utmost to extend their useful lifetime. This means we must stop misusing them. Consider the case of penicillin. For decades, it has been prescribed by many physicians for every sniffle and sneeze, even when the source of the problem was a virus. Antibiotics have been recklessly prescribed for ear and even sinus infections, many of which, as Mayo Clinic researchers recently noted, are not due to bacteria at all but to the immune system's response to fungal infections (see box).
To make matters worse, antimicrobials have been introduced into hand creams, household cleansers, livestock feed. Not long ago, the FDA's Center for Veterinary Medicine announced plans to withdraw approval of the use of fluoroquinolones in poultry feed. Of particular concern was campylobacter, a common cause of diarrheal disease. And the Minnesota department of public health made headlines when it surveyed poultry on sale in the state's supermarkets and found 88% of the samples were contaminated by campylobacter, 20% of which were fluoroquinolone resistant.
Overuse is just part of the problem, however. The evolution of resistance really goes into fast-forward when patients with serious diseases like malaria and TB do not follow doctor's orders, often because they are poor and cannot afford a full course of medication. Instead, they take just enough medication to alleviate their symptoms but not enough to rid their system of the original infection. This has the effect of eliminating the drug-sensitive microbes from the lineup and encouraging the drug-resistant ones to grow.