http://www.usnews.com/usnews/issue/990510/nycu/antibiotic.htm
Losing the Battle of the Bugs

excerpt:
The latest turn in the battle of the bugs is no surprise. Scientists have known since the dawn of the antibiotic age in the 1940s that the more an antibiotic is used, the quicker it becomes useless. That's because of natural selection: While most bacteria exposed to the drug are killed, the fittest survive and pass survival traits to their offspring. With continued use of the antibiotic, the resistant bugs proliferate. Bacteria have a broad array of tactics to combat antibiotics' toxicity, and they can give the genes that control these feats to nearby, even unrelated, bugs.