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Acid-fastness is a physical property of certain
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
l and
eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...
s, as well as some sub-cellular structures, specifically their resistance to decolorization by
acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a se ...
s during laboratory
staining Staining is a technique used to enhance contrast in samples, generally at the microscopic level. Stains and dyes are frequently used in histology (microscopic study of biological tissues), in cytology (microscopic study of cells), and in th ...
procedures. Once stained as part of a sample, these organisms can resist the acid and/or ethanol-based decolorization procedures common in many staining protocols, hence the name ''acid-fast''. The mechanisms of acid-fastness vary by species, although the most well-known example is in the genus ''
Mycobacterium ''Mycobacterium'' is a genus of over 190 species in the phylum Actinomycetota, assigned its own family, Mycobacteriaceae. This genus includes pathogens known to cause serious diseases in mammals, including tuberculosis ('' M. tuberculosis'') ...
'', which includes the species responsible for
tuberculosis Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, ...
and
leprosy Leprosy, also known as Hansen's disease (HD), is a long-term infection by the bacteria '' Mycobacterium leprae'' or '' Mycobacterium lepromatosis''. Infection can lead to damage of the nerves, respiratory tract, skin, and eyes. This nerve d ...
. The acid-fastness of ''Mycobacteria'' is due to the high mycolic acid content of their
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mec ...
s, which is responsible for the staining pattern of poor absorption followed by high retention. Some bacteria may also be partially acid-fast, such as ''
Nocardia ''Nocardia'' is a genus of weakly staining Gram-positive, catalase-positive, rod-shaped bacteria. It forms partially acid-fast beaded branching filaments (acting as fungi, but being truly bacteria). It contains a total of 85 species. Some sp ...
''. Acid-fast organisms are difficult to characterize using standard microbiological techniques, though they can be stained using concentrated dyes, particularly when the staining process is combined with heat. Some, such as ''Mycobacteria'', can be stained with the
Gram stain In microbiology and bacteriology, Gram stain (Gram staining or Gram's method), is a method of staining used to classify bacterial species into two large groups: gram-positive bacteria and gram-negative bacteria. The name comes from the Danish b ...
, but they do not take the crystal violet well and thus appear light purple, which can still potentially result in an incorrect gram negative identification. The most common staining technique used to identify acid-fast bacteria is the
Ziehl–Neelsen stain Ziehl–Neelsen staining is a type of acid-fast stain, first introduced by Paul Ehrlich. Ziehl–Neelsen staining is a bacteriological stain used to identify acid-fast organisms, mainly Mycobacteria. It is named for two German doctors who modi ...
, in which the acid-fast species are stained bright red and stand out clearly against a blue background. Another method is the Kinyoun method, in which the bacteria are stained bright red and stand out clearly against a green background. Acid-fast ''Mycobacteria'' can also be visualized by fluorescence microscopy using specific fluorescent dyes ( auramine-rhodamine stain, for example). The eggs of the parasitic lung fluke '' Paragonimus westermani'' are actually destroyed by the stain, which can hinder diagnosis in patients who present with TB-like symptoms.


Some acid-fast staining techniques

*
Ziehl–Neelsen stain Ziehl–Neelsen staining is a type of acid-fast stain, first introduced by Paul Ehrlich. Ziehl–Neelsen staining is a bacteriological stain used to identify acid-fast organisms, mainly Mycobacteria. It is named for two German doctors who modi ...
(classic and modified bleach types) * Kinyoun stain * For color blind people (or in backgrounds where detecting red bacteria is difficult), Victoria blue can be substituted for carbol fuchsin and
picric acid Picric acid is an organic compound with the formula (O2N)3C6H2OH. Its IUPAC name is 2,4,6-trinitrophenol (TNP). The name "picric" comes from el, πικρός (''pikros''), meaning "bitter", due to its bitter taste. It is one of the most acidic ...
can be used as the counter stain instead of
methylene blue Methylthioninium chloride, commonly called methylene blue, is a salt used as a dye and as a medication. Methylene blue is a thiazine dye. As a medication, it is mainly used to treat methemoglobinemia by converting the ferric iron in hemoglobin ...
, and the rest of the Kinyoun technique can be used. ** Various bacterial spore staining techniques using Kenyon e.g. *** Moeller's method *** Dorner's method (acid alcohol decolorizer) without the Schaeffer–Fulton modification (decolorize by water) *** Detergent method, using Tergitol 7, nonionic polyglycol ether surfactants type NP-7 * Fite stain ** Fite-Faraco stain ** Wade Fite stain * Ellis and Zabrowarny stain (no phenol/carbolic acid) * Auramine-rhodamine stain * Auramine phenol stain


Notable acid-fast structures

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 ''Mycobacterium'' is a genus of over 190 species in the phylum Actinomycetota, assigned its own family, Mycobacteriaceae. This genus includes pathogens known to cause serious diseases in mammals, including tuberculosis ('' M. tuberculosis'') and ...
– ''M. tuberculosis'', ''M. leprae'', ''M. smegmatis'' and atypical ''Mycobacterium'' *
Actinomycetes The Actinomycetales is an order of Actinomycetota. A member of the order is often called an actinomycete. Actinomycetales are generally gram-positive and anaerobic and have mycelia in a filamentous and branching growth pattern. Some actinomycete ...
(especially some aerobic ones) with mycolic acid in their cell wall (note ''Streptomyces'' do NOT have); not to be confused with ''
Actinomyces ''Actinomyces'' is a genus of the Actinomycetia class of bacteria. They all are gram-positive. ''Actinomyces'' species are facultatively anaerobic and they grow best under anaerobic conditions. ''Actinomyces'' species may form endospores, an ...
'', which is a non-acid-fast genus of
actinomycete The Actinomycetales is an order of Actinomycetota. A member of the order is often called an actinomycete. Actinomycetales are generally gram-positive and anaerobic and have mycelia in a filamentous and branching growth pattern. Some actinomycete ...
**''Nocardia'' (weakly acid-fast; resists decolorization with weaker acid concentrations) ** '' Rhodococcus'' ** '' Gordonia'' (an actinomycete) ** '' Tsukamurella'' ** '' Dietzia'' * Head of
sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, ...
* Bacterial spores, see
Endospore An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., n ...
* '' Legionella micdadei'' * Certain cellular inclusions e.g. ** Cytoplasmic
inclusion bodies Inclusion bodies are aggregates of specific types of protein found in neurons, a number of tissue cells including red blood cells, bacteria, viruses, and plants. Inclusion bodies of aggregations of multiple proteins are also found in muscle cells ...
seen in *** Neurons in layer 5 of cerebral cortex
neuronal ceroid lipofuscinosis Neuronal ceroid lipofuscinosis is the general name for a family of at least eight genetically separate neurodegenerative lysosomal storage diseases that result from excessive accumulation of lipopigments ( lipofuscin) in the body's tissues. These ...
(
Batten disease Batten disease is a fatal disease of the nervous system that typically begins in childhood. Onset of symptoms is usually between 5 and 10 years of age. Often, it is autosomal recessive. It is the common name for a group of disorders called the n ...
). ** Nuclear inclusion bodies seen in ***
Lead poisoning Lead poisoning, also known as plumbism and saturnism, is a type of metal poisoning caused by lead in the body. The brain is the most sensitive. Symptoms may include abdominal pain, constipation, headaches, irritability, memory problems, infertil ...
*** Bismuth poisoning. * Oocysts of some coccidian parasites in faecal matter, such as: ** ''
Cryptosporidium parvum ''Cryptosporidium parvum'' is one of several species that cause cryptosporidiosis, a parasitic disease of the mammalian intestinal tract. Primary symptoms of ''C. parvum'' infection are acute, watery, and nonbloody diarrhea. ''C. parvum'' in ...
'', ** '' Isospora belli'' ** '' Cyclospora cayetanensis''. * A few other parasites: ** '' Sarcocystis'' ** ''
Taenia saginata ''Taenia saginata'' (synonym ''Taeniarhynchus saginatus''), commonly known as the beef tapeworm, is a zoonotic tapeworm belonging to the order Cyclophyllidea and genus ''Taenia''. It is an intestinal parasite in humans causing taeniasis (a typ ...
'' 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,Wages ds, Wear dJ. acid-fastness of fungi in blastomycosis and histoplasmosis. Arch Pathol Lab Med 1982; 106:440-41. 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


Online protocol examples


Ziehl–Neelsen
protocol (
PDF Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. ...
format). * Alternat
Ellis & Zabrowarny method
for staining AFB. {{DEFAULTSORT:Acid-Fast Bacteria Staining