Cultures often require 24 or more hours before a pathogen can be recovered. A Gram stain can give preliminary information about the type of bacterial and/or fungal organisms that are present.
A rapid diagnosis of bacterial meningitis, made after examining a gram-stained smear of the patient's cerebrospinal fluid, allows the physician to begin treatment immediately.
Intracellular gram-negative diplococci observed in a male urethral specimen may be confirmatory of the diagnosis of gonorrhea. Cultures may not even be needed unless susceptibilities are required. (In the female genital specimen, the presence of gram-negative diplococci is not specific enough to confirm the diagnosis, and a culture or other confirmatory testing must be performed).