A major aim of clinical microbiologists over the last century has been to demonstrate the presence of pathogenic microorganisms in clinical or pathologic samples associated with infectious diseases. With the development of molecular genetics over the last two decades, new technologies have become available that allow more sensitive and specific determinations to be made in shorter periods. Two considerable benefits have accrued: Epidemiologists are now capable of judging clonality among various clinical isolates more powerfully, permitting added accuracy in the evaluation of the epidemic spread of microbes, and clinicians have gained enormous ability to diagnose previously difficult-to-detect pathogens.