Your patient complains of an “itching rash” on her abdomen. On examination, you find that the lesions are red, circular, with a vesiculated border and a healing central area. You suspect tinea corporis. Of the following choices, the MOST appropriate laboratory procedure to make the diagnosis is a:

  •  Fourfold rise in antibody titer against the organism
  •  Fluorescent antibody stain of the vesicle fluid
  •  Giemsa stain for multinucleated giant cells
  •  Potassium hydroxide mount of skin scrapings