Final answer:
Mycobacterium tuberculosis appears as a grouping of massed filaments called cords that are red in color due to fast staining.
Step-by-step explanation:
When infected tissue is stained in a special way and observed under the microscope, Mycobacterium tuberculosis appears as a grouping of massed filaments called cords that are red in color due to fast staining. This staining procedure, known as acid-fast staining, is used to visualize the bacteria because of its waxy mycolic acid coat which blocks penetration by Gram stain reagents. M. tuberculosis is the causative agent of tuberculosis, a chronic granulomatous disease that primarily affects the lungs but can infect other parts of the body as well.