What is behind antibiotic resistance?

Antibiotic resistance develops among bacterial species just as Darwin might have predicted-that is, through natural selection. Because bacterial species can share DNA by a variety of mechanisms, and because some of these microbes are inherently resistant to one or more major antibiotics, we should not be surprised that clinically important species of bacteria can become resistant to commonly used antibiotics by chance alone. The rapid increase in the percentage of strains resistant to one or more antibiotics, especially broad-spectrum agents, may be the result of increased use of such compounds.