Rapid identification of the invading microorganism

In the past several years, many new laboratory procedures have been introduced for the rapid identification of specific microorganisms within various body fluids. These new laboratory procedures have proved to be effective when used in conjunction with, and not to the exclusion of, classic microbiologic techniques. A gram stain of any body fluid, such as cerebrospinal fluid or an aspirate from a septic joint, may provide very important diagnostic information rapidly and may allow preliminary identification of the particular organism responsible for the infection. However, the gram stain is subject to misinterpretation, particularly in inexperienced hands, and thus may provide unreliable information. In addition, prior treatment with antimicrobial agents may alter gram stain findings as well as culture results. With many of the newer laboratory techniques, prior antibiotic therapy does not alter results. Moreover, some of these techniques may provide useful prognostic information by additional semiquantitative modifications. We will describe some of these new laboratory techniques, summarize clinical studies utilizing them, and point out the advantages and disadvantages.