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. • Certain
Actinobacteria (especially aerobic ones in the order
Mycobacteriales) with mycolic acid in their cell wall; not to be confused with
Actinomyces, which is a non-acid-fast genus of
actinomycete. Note that
Streptomyces do not contain mycolic acid. •
Nocardia (weakly acid-fast; resists decolorization with weaker acid concentrations) •
Rhodococcus •
Gordonia •
Tsukamurella •
Dietzia • Head of
sperm • Bacterial spores, see
Endospore •
Legionella micdadei • Certain cellular inclusions e.g. • Cytoplasmic
inclusion bodies seen in • Neurons in layer 5 of cerebral cortex
neuronal ceroid lipofuscinosis (
Batten disease). • Nuclear inclusion bodies seen in •
Lead poisoning • Bismuth poisoning. • Oocysts of some
coccidian parasites in faecal matter, such as: •
Cryptosporidium parvum, •
Isospora belli •
Cyclospora cayetanensis. • A few other parasites: •
Sarcocystis •
Taenia saginata eggs stain well but
Taenia solium eggs don't (can be used to distinguish) •
Hydatid cysts, especially their "
hooklets" stain irregularly with ZN stain but emanate bright red fluorescence under green light, and can aid detection in moderately heavy backgrounds or with scarce hooklets. • Fungal yeast forms are inconsistently stained with Acid-fast stain which is considered a narrow spectrum stain for fungi. In a study on acid-fastness of fungi, 60% of blastomyces and 47% of histoplasma showed positive cytoplasmic staining of the yeast-like cells, and Cryptococcus or candida did not stain, and very rare staining was seen in Coccidioides endospores. ==References==