Discovering new pathogens: culture-resistant bacteria.

Recent advances in gene-amplification technology and molecular phylogenetics have provided the means of detecting and classifying bacteria directly from their natural habitats without the need for culture. These techniques have revolutionized environmental microbiology, and it is now apparent that the global diversity of microorganisms is much greater than previously thought. In the context of clinical microbiology, this molecular-based approach has facilitated the characterization of culture-resistant bacteria associated with human disease. Examples include Helicobacter heilmannii, a cause of gastritis, Tropheryma whippeli (the agent of Whipple's disease), and the agents of human ehrlichiosis and bacillary angiomatosis. Molecular-based techniques also provide a means of investigating complex bacterial flora within the human ecosystem, such as feces and dental plaque, without the bias of culture-based isolation. This has given a new perspective to the study of polymicrobial infections such as gingivitis, and offers the potential for the detection and identification of novel bacterial pathogens from among complex and numerous endogenous microbial flora.