Final answer:
Mycobacterium is resistant to staining due to the presence of mycolic acid-rich cell walls.
Step-by-step explanation:
The Mycobacterium genus contains bacteria with mycolic acid-rich cell walls, which make them resistant to staining. The waxy mycolic acid acts as a barrier, preventing stains from penetrating the cell. This is why the Gram stain does not work with mycobacteria such as Mycobacterium. Instead, the acid-fast staining technique is used to identify the presence of mycolic acid-rich cell walls in bacterial samples.