Nocardia

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Nocardia
Close-up image of a Nocardia species culture on sheep blood agar
Scientific classification Edit this classification
Domain: Bacteria
Phylum: Actinomycetota
Class: Actinomycetia
Order: Mycobacteriales
Family: Nocardiaceae
Genus: Nocardia
Trevisan 1889 (Approved Lists 1980)
Type species
Nocardia asteroides
(Eppinger 1891) Blanchard 1896 (Approved Lists 1980)
Species

See text.

Synonyms[1]
  • Micropolyspora Lechevalier et al. 1961 (Approved Lists 1980)
  • Asteroides Puntoni & Leonardi, 1935
  • Proactinomyces (K.Lehmann & Haag) H.L.Jensen, 1934[2]
Nocardia as found on a brain biopsy.

Nocardia is a

acid-fast beaded branching filaments (acting as fungi, but being truly bacteria). It contains a total of 85 species. Some species are nonpathogenic, while others are responsible for nocardiosis.[3] Nocardia species are found worldwide in soil rich in organic matter. In addition, they are oral microflora found in healthy human gingiva, as well as periodontal pockets.[4] Most Nocardia infections are acquired by inhalation of the bacteria or through traumatic introduction through openings in epithelial barriers
.

Culture and staining

Nocardia colonies have a variable appearance, but most species appear to have aerial

acid-fast (meaning a less concentrated solution of sulfuric or hydrochloric acid should be used during the staining procedure) due to the presence of intermediate-length mycolic acids in their cell wall. Majority of strains possess the cord factor
(trehalose 6-6' dimycolate), an important virulence factor.

Four different Nocardia species on sheep blood agar demonstrating different colouring

They are catalase positive and can grow easily on the most commonly used media with colonies becoming evident in 3–5 days. However, prolonged incubation periods (2–3 weeks) are sometimes needed.

Nocardia asteroides

Virulence

The various species of Nocardia are

macrophages by preventing the fusion of the phagosome with the lysosome).[citation needed
]

An important virulence factor in many pathogenic strains of Nocardia is

trehalose dimycolate, which is also found in the bacterial genus Mycobacterium. This toxin can cause cachexia, a form of muscle wasting.[5]

Clinical disease and microbiological diagnosis

The most commonly encountered species are Nocardia brasiliensis, Nocardia cyriacigeorgica, Nocardia farcinica, and Nocardia nova. Nocardia asteroides is most frequently found species causing noncutaneous invasive disease. Most cases occur as an opportunistic infection in immunocompromised patients. N. brasiliensis is the most common species causing cutaneous nocardiosis. N. caviae is another species of medical interest. The genus is acid-fast to some degree, it stains only weakly Gram positive.

The most common form of human nocardial disease is a slowly progressive

pleura or chest wall. Pre-existing pulmonary disease, especially pulmonary alveolar proteinosis
, increases the risk of contracting a Nocardia pneumonia. Every organ can be affected if a systemic spread takes place.

Nocardia species are deeply involved in the process of encephalitis as one of its main pathogenic effects. In about 25–33% of people Nocardia infection takes the form of encephalitis and/or brain abscess formation. Nocardia may also cause a variety of cutaneous infections such as actinomycetoma (especially N. brasiliensis), lymphocutaneous disease, cellulitis, and subcutaneous abscesses.[6]

Nocardia isolation from biological specimens can be performed using an agar medium enriched with yeast extract and

activated charcoal
(BCYE), the same used for Legionella species. Selective media for mycobacteria or fungi can also be inoculated. The most suitable specimens are the sputum, or when clinically necessary, bronchoalveolar lavage or biopsy. Further biochemical tests for species identification are not routinely performed. Serological or cutaneous tests are not available.

Treatment

In most patients with Nocardia infection, the combination of antibiotics is needed.[7]

trimethoprim-sulfamethoxazole, is the treatment of choice.[8] People who take trimethoprim-sulfamethoxazole for other reasons, such as prevention of Pneumocystis jirovecii infection, appear to have fewer Nocardia infections,[9] although this protective effect has been considered unreliable,[10] and some studies have disputed it altogether.[11] Minocycline is usually substituted when a sulfa cannot be given; high-dose imipenem and amikacin have also been used in severe or refractory cases.[8] Linezolid appears to be highly effective against Nocardia, but it is very expensive and may cause severe adverse effects.[12]

Antibiotic therapy is continued for six months (in immunocompetent people) to a year (in immunosuppression), and may need to be continued indefinitely.[8] Proper wound care is also critical.

Genetics

Although Nocardia has interesting and important features such as production of antibiotics and aromatic compound-degrading or -converting enzymes, the genetic study of this organism has been hampered by the lack of genetic tools. However, practical Nocardia–E. coli shuttle vectors have been developed recently.[13]

The genera Nocardia and Rhodococcus have been found to be closely related, supported by two

acetyl coenzyme A carboxylase (ACC), and a three-amino-acid insertion in a conserved region of an ATP-binding protein that are specifically shared by species from these two genera. In addition, 14 hypothetical conserved signature proteins have been identified which are unique to the genera Nocardia and Rhodococcus.[14]

Species

Nocardia comprises the following species:[1]

Nomenclature

The genus was named for Edmond Nocard (1850-1903), a French 19th-century veterinarian and biologist.[15]

The genus was circumscribed by Vittore Benedetto Antonio Trevisan di Saint-Léon in Ann. Inst. Pasteur vol.2 (Issue 6) on page 295 in 1888.[2]

References

  1. ^ a b Euzéby JP, Parte AC. "Nocardia". List of Prokaryotic names with Standing in Nomenclature (LPSN). Retrieved June 25, 2022.
  2. ^ a b "Nocardia Trevisan, 1889". www.gbif.org. Retrieved 24 August 2022.
  3. ISBN 0-8385-8529-9
    .
  4. ^ "Nocardia species". GlobalRPH. Retrieved 2023-06-28.
  5. ISSN 1350-0872
    .
  6. PMID 35693062
    .
  7. PMID 32415818
    .
  8. ^ a b c Bartlett JG (October 5, 2007). "Nocardia". Point-of-Care Information Technology ABX Guide. Johns Hopkins University. Archived from the original on December 1, 2009. Retrieved on January 3, 2009. Freely available with registration.
  9. PMID 9413427
    .
  10. PMID 17443467
    .
  11. PMID 18435787
    .
  12. S2CID 33975237
    .
  13. PMID 17314425. Archived from the original
    on 2007-08-17.
  14. PMID 22390973
    .
  15. ISBN 978-3-946292-41-8
    . Retrieved January 27, 2022.

Further reading

External links
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