Final answer:
The abbreviation for 'acid-fast bacillus' is AFB, referring to the bacteria that cause tuberculosis, such as Mycobacterium tuberculosis. They are detected using the Ziehl-Neelsen acid-fast staining technique and are important in diagnosing tuberculosis.
Step-by-step explanation:
The abbreviation for the phrase acid-fast bacillus which exists in Tuberculosis is AFB. This term refers to the bacteria that cause tuberculosis, known as Mycobacterium tuberculosis. Acid-fast bacilli are distinguished by their unique cell walls rich in waxy mycolic acids, which render them resistant to certain staining techniques such as Gram staining. Instead, the Ziehl-Neelsen acid-fast staining technique is used to visualize these bacteria by staining them red, while the background or other non-acid-fast cells are stained blue. AFB can be observed in sputum smears under the microscope, and their presence suggests the need for further diagnostic procedures, such as culture and nucleic acid hybridization, to confirm an M. tuberculosis infection.