An acid-fast stain is used to detect which genera, and what cell-wall feature allows this staining?

• A. To identify Gram-negative enteric bacteria by lipopolysaccharide.
• B. To detect Mycobacterium and Nocardia due to waxy mycolic acids in their cell walls.
• C. To differentiate cocci from rods.
• D. To visualize spores within Bacillus and Clostridium.

Answer: (B)