Nocardia
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 Nocardia asteroides (yellow colonies).
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Nocardia is a genus of Gram-positive, catalase-positive, rod-shaped bacteria; some species are pathogenic (nocardiosis).[1] Nocardia are found worldwide in soil that is rich with organic matter. Most Nocardia infections are acquired by inhalation of the bacteria or through traumatic introduction.
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[edit] Culture and staining
Nocardia colonies have a variable appearance, but most species appear to have aerial hyphae when viewed with a dissecting microscope, particularly when they have been grown on nutritionally-limiting media. Nocardia grow slowly on non-selective culture media, and are strict aerobes with the ability to grow in a wide temperature rang. Some species are partially acid fast due to the presence of intermediate-length mycolic acids in their cell wall.
[edit] Virulence
Nocardia are opportunistic pathogens, causing disease primarily among the young, the elderly, and those who are immunocompromised. These bacteria secrete various proteins (virulence factors) that increase their pathogenicity: factors include cord factor, catalase, and superoxide dismutase. Cord factor aids Nocardia survival by interfering with phagocytosis by macrophages. It does this by preventing the fusion of the phagosome with the lysosome. Catalase and superoxide dismutase which inactivate oxygen metabolites (e.g. hydrogen peroxide and superoxide) that are toxic to bacteria.
[edit] Clinical disease
Nocardia asteroides is the species of Nocardia that is most commonly associated with human disease. Disease by these bacteria in humans is primarily opportunistic, occurring in immunocompromised patients. Pre-existing lung disease, especially alveolar proteinosis, increases one's risk of contracting a Nocardia infection.
Pneumonia caused by Nocardia is difficult to distinguish from that caused by other microorganisms. One distinguishing characteristic, however, is that it is relatively slow-growing. Common symptoms include cough, difficulty breathing (dyspnea), and fever. It is not uncommon for this infection to spread to the pleura.
Nocardia is responsible for a variety of cutaneous infections such as mycetoma, lymphocutaneous disease, cellulitis and subcutaneous abscesses, and madura foot. A mycetoma is a tumor-like mass that results from cutaneous infection and is characterized by suppurative granulomas, and progressive fibrosis and necrosis. The most common causative organism for this is N. brasiliensis. Madura foot is a chronic infection of the bones and soft tissues of the foot that can cause gross deformity. It most commonly occurs in Sudan, north Africa, and the west coast of India among people who walk barefoot. A common causative organism is Actinomadura madurae, formerly classified with the nocardiae as N. madurae.
About one-third of people with Nocardia infection will have involvement of the central nervous system. This usually results in headache, and fever, possibly along with other deficits. These symptoms are due to abscesses in the brain caused by bacterial infection.
[edit] Treatment
Antibiotic therapy with a sulfonamide is the treatment of choice. The most common sulfonamide used is trimethoprim-sulfamethoxazole. People who take trimethoprim-sulfamethoxazole for other reasons, such as prevention of pneumocystis jiroveci infection in AIDS, have fewer nocardia infections. High-dose imipenem and amikacin have also been used in refractory cases. Antibiotic therapy may have to be continued for six months to a year. Proper wound care is also critical.
[edit] Genetics
Despite that 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.[2]
[edit] References
- ^ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill, pp. 460–2. ISBN 0838585299.
- ^ Chiba K, Hoshino Y, Ishino K, Kogure T, Mikami Y, Uehara Y, Ishikawa J (2007). "Construction of a Pair of Practical Nocardia-Escherichia coli Shuttle Vectors". Jpn J Infect Dis 60 (1): 45-7. PMID 17314425.
[edit] Further reading
- Ishikawa J, Yamashita A, Mikami Y, Hoshino Y, Kurita H, Hotta K, Shiba T, Hattori M (2004). "The complete genomic sequence of Nocardia farcinica IFM 10152". Proc Natl Acad Sci U S A 101 (41): 14925-30. PMID 15466710.
- Arceneaux, Jean. "Corynebacterium and Related Genera." Lecture to 2nd Year Medical Students at University of Mississippi Medical Center. 10/04/05.
- Greenwood, David, Richard C.B. Slack, and John F. Peutherer. Medical Microbiology: A Guide to Microbial Infections, 16th ed. (2002). ISBN 0-443-07077-6
