Penicilin Resistant Staphylococcus

Another prime example of selection is resistance to penicillin. When it was introduced in the early 1940s, penicillin was a miracle drug, especially effective at curing infections caused by the bacteria Staphylococcus aureus (“staph”). In 1941, the drug could wipe out every strain of staph in the world. Now, seventy years later, more than 95 percent of staph strains are resistant to penicillin. What happened was that mutations occurred in individual bacteria that gave them the ability to destroy the drug, and of course these mutations spread worldwide. In response, the drug industry came up with a new antibiotic, methicillin, but even that is now becoming useless due to newer mutations. In both cases, scientists have identified the precise changes in the bacterial DNA that conferred drug resistance.

Jerry A. Coyne, Why Evolution Is True (January 22, 2009)

• evolution
• resistance