PowerPoint Contents
Mycobacterium tuberculosis (Enlarged view)Slide 1. Mycobacterium tuberculosis
Occasionally, mycobacteria are visible on a Gram stain as gram-positive or gram-variable curved, beaded bacilli. When slightly out of focus, like the bacilli in the lower right (arrow on the labeled slide), mycobacteria have a characteristic refractile appearance, presumably because of their waxy cell walls.
Mycobacterium tuberculosis (Labeled view)
(Labeled view)
Mycobacterium tuberculosis (Enlarged 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.
Mycobacterium tuberculosis (Enlarged view)
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).
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