Rapid and reliable techniques for the laboratory detection of bacterial meningitis

Microorganisms encountered in cerebrospinal fluid require rapid and accurate means of detection and identification in the laboratory. Although restricted to morphologic study and Gram reaction, the Gram stain of cerebrospinal fluid has been the primary diagnostic tool for preliminary diagnosis of purulent meningitis, with identification of the etiologic agent often made within one to two hours by direct microscopic examination. Gram stain and appropriate culture procedures still provide the basis for comparing other diagnostic methods. Nonimmunologic methods that show promise in being both rapid and reliable include gas-liquid chromatography and the Limulus amebocyte lysate test. Fatty acid and carbohydrate profiles characteristic of Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis, and Staphylococcus aureus in the cerebrospinal fluid of human subjects and animals have been obtained by gas-liquid chromatography. Also, a unique compound has been detected by gas-liquid chromatography in cerebrospinal fluid from patients with tuberculous meningitis. The Limulus test has been reliable in spinal fluid and almost always gives positive results in H. influenzae and other Gram-negative meningitides. Nonspecific test procedures of varying degrees of accuracy and promise include lactic acid, C-reactive protein, and lactate dehydrogenase determination. Direct microscopic examination of cerebrospinal fluid remains the most practical and accurate method for identifying the etiologic basis of bacterial (and fungal) meningitis.