Molecular bacteriology: a diagnostic tool for the millennium.

From a practical viewpoint, clinical bacteriology can be subdivided into three main activities. First and foremost is detection, isolation, and identification of pathogens. This is usually achieved by culture of specimens on specific media in defined conditions, accompanied by microscopy and tests of biochemical activity of an isolate. Second is the determination of antibiotic susceptibility, and occasionally, strain markers of clinical relevance—for example, serotypes, toxins, and so on. The third activity is epidemiological identification or comparison of isolates of the same species for infection control or population analysis. This has, until recently, been the preserve of the reference laboratory but devolution of increasingly complex techniques to diagnostic settings is gathering pace. In this article we review some areas in which molecular techniques are being applied for laboratory diagnosis and we examine developments in two basic strategies for test development and the technology required for their delivery to the laboratory bench.