What is the primary infectious agent that causes tuberculosis?

• A. Staphylococcus aureus
• B. Escherichia coli
• C. Streptococcus pneumoniae
• D. Mycobacterium tuberculosis

Answer: (D)

Tuberculosis is caused by a single infectious agent: Mycobacterium tuberculosis. This bacterium is an acid-fast, slow-growing bacillus with a waxy cell wall rich in mycolic acids, which helps it resist drying and makes it difficult to stain with standard methods. It becomes airborne when someone with active TB coughs or sneezes, and inhaled bacteria lodge in the lungs, triggering a granulomatous inflammatory response that can lead to caseating granulomas and latent or active infection. Among common pathogens, only Mycobacterium tuberculosis is linked to tuberculosis; the others are associated with different infections such as skin infections, urinary/enteric infections, or general pneumonia, not TB.