Bacilli that hold stain colour even after washing with acid. Tubercle bacilli are acid-fast bacilli

Rod-shaped bacteria that hold stain colour even after washing with acid. Tubercle bacilli are acid-fast bacilli

Microorganisms that are distinguished by their retention of specific stains even after being rinsed with an acid solution. The majority of AFB in patient specimens are mycobacteria, including species other than Mycobacterium tuberculosis complex. A positive nucleic acid amplification (NAA) or culture result is needed for confirmation of M. tuberculosis complex. The relative concentration of AFB per unit area on a slide (the smear grade) is associated with infectiousness

Microorganisms that retain certain applied stains after being rinsed with an acid solution. Most acid-fast organisms detected in patient specimens are mycobacteria. When AFB are seen on a stained smear of sputum or other specimen, a diagnosis of TB disease should be suspected, and the concentration of organisms per unit area of slide (the smear grade) correlates with the degree of infectiousness

Rod-shaped bacteria that do not lose their stain when exposed to acid or acid–alcohol mixture after the staining process, i.e. bacteria of the Mycobacterium tuberculosis complex and all non-tuberculous mycobacteria