(Labeled view)

Slide 2. Mycobacterium tuberculosis
With the Ziehl-Neelsen stain, the appearance of Mycobacterium tuberculosis bacilli as red bacilli on a blue background indicates that they are acid fast. Many organisms are curved and some are beaded. In general, mycobacteria range from coccobacilli to long, slender, curved rods that may have beads or bands within them. To distinguish among mycobacteria on the basis of their microscopic appearance is difficult, although some species are often thicker, longer, shorter, or more coarsely beaded
than is M. tuberculosis.

Slide 3. Mycobacterium tuberculosis
With fluorescent microscopic examination, auramine O (a nonimmunologic stain taken up by mycobacteria) fluoresces, and the bacilli appear as yellow rods. The fluorescent technique reduces the time required to examine smears for mycobacteria because slides can be scanned rapidly at a lower magnification (500x).