Antibiotics were invented by bacteria and fungi during thier conception in this universe. Used to control microbial niche environments, it wasn't until 1928 that Fleming (and subsequently Florey and Chain) began the widespread use of the antibiotic penicillin to control bacterial infections in humans. And so, the antibiotic revolution began.
Subsequent use (and misuse) of antibiotics has given rise to various resistant strains. These are becoming a vast problem in the treatment of diseases that once were "easily" curable, including the well-publisized MRSA and XDR-TB, as well as many others.
This paper, coming out of Harvard University, describes the isolation of bacterial strains that can live on antibiotics as their sole carbon source. Current thought states that resistance in a bacterial population occurs because of exposure in clinical settings (or a popular theme of dumping antibiotics down the drain). However, the authors show that even secluded environmental isolates have the ability to subsist on both natural and synthetic antibiotics.
Our antibiotics are just variations on themes we have seen in nature, and because of this, the environment represents a vast source of antibiotic resistance mechanisms that we have yet to discover. In niches exposed to antibiotics (ie. clinical pathogens) complete resistance is preferential. However, antibiotic metabolism (as described in this paper) would confer an advantage, even if it is only small in comparison.
I find it fascinating that in 11 different soils (urban, farm, and pristine), bacteria were present that could thrive on 18 different antibiotics as carbon sources! These bugs were not just living with the antibiotics, but were actually eating them!
We have much more to discover about antibiotic resistance mechanisms, this study clearly shows a direction that we can head to begin this task. Just as we looked to nature to develop antibioitcs, so must we look to nature to study how resistance works.
Dantas, G., Sommer, M.O., Oluwasegun, R.D., Church, G.M. (2008). Bacteria Subsisting on Antibiotics. Science, 320(5872), 100-103. DOI: 10.1126/science.1155157
Timebomb : The Global Epidemic of Multi-Drug Resistant Tuberculosis
Good Germs, Bad Germs: Health and Survival in a Bacterial World
Teaming with Microbes: A Gardener's Guide to the Soil Food Web