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Very few structures are acid-fast; this makes staining for acid-fastness particularly useful in diagnosis. The following are notable examples of structures which are acid-fast or modified acid-fast: All Mycobacteria – M. tuberculosis, M. leprae, M. smegmatis and atypical mycobacteria.
The acid-fast staining method, in conjunction with auramine phenol staining, serves as the standard diagnostic tool and is widely accessible for rapidly diagnosing tuberculosis (caused by Mycobacterium tuberculosis) and other diseases caused by atypical mycobacteria, such as leprosy (caused by Mycobacterium leprae) and Mycobacterium avium ...
The Kinyoun method can be modified as a weak acid fast stain, which uses 0.5–1.0% sulfuric acid instead of hydrochloric acid.The weak acid fast stain, in addition to staining Mycobacteria, will also stain organisms that are not able to maintain the carbol fuchsin after decolorizing with HCl, such as Nocardia species and Cryptosporidium.
Mycobacterium tuberculosis (M. tb), also known as Koch's bacillus, is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. [ 1 ] [ 2 ] First discovered in 1882 by Robert Koch , M. tuberculosis has an unusual, waxy coating on its cell surface primarily due to the presence of mycolic acid .
Since this genus has cell walls with a waxy lipid-rich outer layer containing high concentrations of mycolic acid, [4] acid-fast staining is used to emphasize their resistance to acids, compared to other cell types. [5] Mycobacterial species are generally aerobic, non-motile, and capable of growing with minimal nutrition.
Mycobacterium smegmatis is an acid-fast bacterial species in the phylum Actinomycetota and the genus Mycobacterium.It is 3.0 to 5.0 μm long with a bacillus shape and can be stained by Ziehl–Neelsen method and the auramine-rhodamine fluorescent method.
It is Gram-positive by Gram staining, but Mycobacterium leprae was traditionally stained with carbol fuchsin in the Ziehl–Neelsen stain. Because the bacilli are less acid-fast than Mycobacterium tuberculosis (MTB), the Fite-Faraco staining method, which has a lower acid concentration, is used now. [9] [10] In size and shape, it closely ...
Mycobacteria have an outer membrane lipid bilayer. [56] If a Gram stain is performed, MTB either stains very weakly "Gram-positive" or does not retain dye as a result of the high lipid and mycolic acid content of its cell wall. [57] MTB can withstand weak disinfectants and survive in a dry state for weeks.