What is the correct sequence of steps in a typical direct fluorescent antibody (FA) test on a patient-derived slide?

• A. Culture the organism from the patient sample for 48 hours, fix the colonies to a slide, then add fluorescently labeled tertiary antibodies that bind to host complement proteins and image under electron microscope.
• B. Add fluorescent secondary antibody to empty slide, air dry, incubate with patient serum, then visualize under brightfield microscopy after Gram staining.
• C. Place patient sample on slide, add fluorescently labeled primary antibodies, wash, then visualize with fluorescence microscope.
• D. Incubate patient serum with enzyme substrate, perform ELISA plate reading, transfer to slide, then confirm with immunoblot to visualize fluorescence.

Answer: (C)