infectious diseases
Microscopy
Introduction
Light microscopy can be done quickly, but accuracy depends on the experience of the microscopist and quality of equipment. Regulations often limit physicians’ use of microscopy for diagnostic purposes outside a certified laboratory. Microscopic examination of tissue may be required to distinguish invasive disease from surface colonization—a distinction not easily achieved by culture methods. Most specimens are treated with stains that color pathogens, causing them to stand out from the background, although Wet mounts of unstained samples can be used to detect fungi and certain other pathogens. The clinician orders a stain based on the likely pathogens. However, no stain is 100% specific (ie, different organisms may stain similarly). Most samples are treated with Gram stain and, if mycobacteria are suspected, with an Because microscopic detection usually requires a microbe concentration of at least about 1×104-5/mL, most body fluid specimens (eg, cerebrospinal fluid) are concentrated (eg, by centrifugation) before examination. 