When evaluating Gram stains of clinical samples, keep in mind the source of material from which the smear was made.
Bacteria found in cerebrospinal fluid (CSF), blood, tissue, and specimens from other sterile sites are always significant. Gram stains of body fluids that are normally sterile must be examined carefully. For every one organism per oil immersion field, there are about 105 organisms per mL present in the sample.
Examining stained smears of CSF sediment may assist the clinician in establishing a presumptive diagnosis. The Gram stain result and the results of other special stains could also guide in the selection of culture media. If bacteria are observed in a CSF specimen, it is important to determine and report whether the bacteria are inside or outside of white blood cells (intracellular or extracellular). The quantity of organisms seen and the amount and type of host cells are also important to report.
Bacteria observed in specimens from the throat, genital tract, and other areas containing normal flora suggest infection only if their composition and type vary significantly from the norm.
