Gram stain reports what bacteria and/or yeast and tissue cells are present, if any. If present, reports include quantity and type of bacteria, yeast, and tissue cells. If absent, reports will state no microorganisms, white blood cells, and/or epithelial cells.
Gram positive = purple (retain purple crystal violet dye after the decolorization step)
Gram negative = red (lose purple dye after the decolorization step and stain with red safranin dye)
No epithelial cells
Numerous Gram positive cocci in clusters
Moderate epithelial cells
Numerous Gram postive cocci in clusters
Moderate Gram negative bacilli
Few Gram poistive cocci in chains
Rare yeast with pseudohyphae
No epithelial cells
No microorganisms seen
Gram stains allow rapid, same-day identification of potential pathogens in specimens, allowing appropriate empiric antibiotic choices to be made. Go to “Gram Stain Results” and “Specimen Gram Stains” to see how the organism descriptions mentioned in the reports above should make you think of specific organisms such as Staphylococcus and Streptococcus, and specific infectious diseases.
If a Gram stain does not show any WBC, epithelial cells or bacteria or yeast, the report will say so as in example 3 above.
In addition, Gram stains permit assessment of the quality of respiratory and exudate/wound specimens based on the number of white blood cells vs. the number of epithelial cells. In an immunocompetent patient, if a specimen represents disease process that specimen should have more white blood cells than epithelial cells. In a severely immunocompromised patient who may not have many white blood cells, a specimen that represents disease process may not have many white blood cells but it should not have high numbers of epithelial cells. The more epithelial cells in a sputum specimen or wound specimen, such as in the second Gram stain example above, the lower the quality of the specimen and the less credence culture results on that specimen should have in patient management.
Also, keep in mind that just because the lab grows an organism does not mean that organism needs to be killed (i.e. the organisms may be commensals or contaminants). Later in the year you will have an on-line self-study session on specimen collection and laboratory results interpretation that should explain this concept in more detail.