NOCARDIA

27 plus species including:

SPECIES

MICROSCOPIC APPEARANCE

Gram Stain: Positive to variable, usually partially acid-fast.
Morphology: Rudimentary to extensively branched vegetative hyphae which fragment in situ or on mechanical disruption into bacteroid, rod-shaped to coccoid elements. Short to long chains of conidia occasionally found on hyphae and substrate hyphae.
Size: 0.5-1.2 micrometers in diameter.
Motility: Non-motile.
Capsules: None.
Spores: No endospores, sporangia, sclerotia, or synnemata are formed.
Other: Aerial hyphae are almost always produced.

MACROSCOPIC APPEARANCE

Colonies have a chalky, mat or velvety appearance. Color may appear brown, tan, pink, orange, red, purple, gray, or white. Texture may be smooth or granular, irregular, wrinkled, or heaped.

METABOLIC PROPERTIES

Aerobic and mesophilic. Chemoorganotrophic, having an oxidative type metabolism.

KEY BIOCHEMICAL REACTIONS

HABITAT

Widely distributed in soil, water, air, sewage, insects and plants, may be present in clinical specimens as opportunistic pathogens.

PATHOGENICITY

Nocardia are usually pathogenic opportunists in humans and animals whose host defenses are compromised. One notable exception is N. brasiliensis which is typically considered an obligatory pathogen.

The basic types of human diseases caused are (a) pulmonary disease, neural and/or systemic nocardiosis (b) actinomycotic mycetomas which are tumor-like growths of the organisms within the tissues; and (c) localized cutaneous or subcutaneous infections which usually represent primary infections.

RECOMMENDED MEDIA

For culture: Lowenstein Jensen Medium.
For selective isolation: Columbia Blood Agar or Sabouraud Dextrose Agar.
For maintenance: Yeast Extract Glucose Agar for short-term maintenance and lyophilization for long-term preservation.

INCUBATION

Temperature: 35 degrees C.
Time: 3-10 days (look for pigmented colonies with downy aerial hyphae).
Atmosphere: Aerobic.

REFERENCES

1. Holt, J.G., et al. 1994. Bergey's Manual of Determinative Bacteriology , 9th ed. Williams & Wilkins, Baltimore, MD.

2. Holt, J.G., et al. 1986. Bergey's Manual of Systemic Bacteriology , Vol. I & II. Williams & Wilkins, Baltimore, MD.

3. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.

4. Murray, P.R., et al. 1995. Manual of Clinical Microbiology , 6th ed. American Society for Microbiology, Washington, D.C.

5. Internet: www.hardlink.com /Bacterial Database Search, February, 1998.

6. Hensyl, B.R., et al. 1990. Stedman's Medical Dictionary , 25th ed. Williams & Wilkins, Baltimore, MD.

7. Koneman, et al. 1997. Color Atlas and Textbook of Diagnostic Microbiology , 5th ed. Lippincott, Philadelphia, PA.


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