The molecular diagnosis of cutaneous infection

Molecular biologic techniques are having an impact on many different aspects of medicine. In the realm of infectious agents, they are enhancing our diagnostic capabilities, allowing earlier detection of infection, avoiding the need of culturing infectious agents for the purpose of diagnosis, and broadening our concepts to include the presence of infection in the absence of a culturable agent or serologic evidence of infection. As one might expect, the applicability of these techniques varies with the type of infectious agent being considered. For example, in most bacterial infections the infectious agent can be cultured and accurately identified within 48 hours. It is therefore unlikely that molecular diagnostic techniques will replace the "gold standard" of culture in instances of bacterial infection. Mycobacterial and spirochetal agents, by contrast, do not fall into this category. Although the rapid growers (Mycobacterium fortuitum and Mycobacterium chelonae) pose little problem because they can be cultured within 1 week, M. tuberculosis, M. leprae and the slow growing mycobacteriae require long intervals to culture and/or identify. These organisms may in the future be identified with molecular diagnostic techniques. In the group of spirochetal pathogens, Treponema pallidum infection is, for the most part, easily diagnosed with serologic studies. In early seronegative cases, spirochetes can be detected in primary inoculation lesions by darkfield microscopy or in tissue sections with appropriate stains. Conversely, detection of Borrelia burgdorferi is currently fraught with difficulties. Tissue sections stained for these spirochetes are difficult to interpret, and serologic studies have shown widely variable results. The polymerase chain reaction has already been applied to the study of Borrelia infection with encouraging early results.