Actinomycetes & Nocardia

A. DESCRIPTION These anaerobic organisms characteristically grow as filamentous branching Gram-positive bacteria. Actinomyces israelii is the etiologic agent for actinomycosis. Some species are members of the normal oral and GI flora.
B. CLINICAL CONSIDERATIONS Cervicofacial infection, usually related to poor dental hygiene, tooth extraction, or some other trauma to the mouth or jaw. Submandibular lesions give the face a swollen, indurated appearance (characteristic). Thoracic and abdominal actinomycoses are more rare and follow aspiration or trauma (including surgery). Chronic endometritis associated with the use of intrauterine contraceptive devices has been described.
C. IDENTIFICATION, CULTURE AND TREATMENT Aerotolerant, but should be cultured under anaerobic conditions. Growth is slow and an extended incubation time is usually required (4-10 days). Most species are nonhemolytic, nonproteolytic, and catalase-negative. "Sulfur granules" are characteristically found in pus from lesions and are diagnostic (actually a mass of Actinomyces filaments solidified with tissue exudates). A clinical diagnosis of actinomycosis is based on: nature of the lesion, slowly progressive course, and history of trauma or predisposing condition. Penicillin G and erythromycin are the DOC for actinomycoses. High doses of penicillin must be used and therapy prolonged for 4 to 6 weeks or longer before any response is seen.

A. DESCRIPTION Gram-positive, rod-shaped with true branching both in culture and in clinical lesions (beaded; sometimes appearing to have alternating G+ and G- sections of the "filament") Commonly found in the environment, particularly in soil. Strict aerobes, weakly acid fast. Even though isolated in small numbers from the respiratory tract of healthy persons, but are not considered members of the normal human flora.

B. CLINICAL CONSIDERATIONS: Nocardiosis Pulmonary Nocardiosis: Acute, chronic, or relapsing broncho-pneumonia (may cause cavitation). Symptoms include cough, shortness of breath (dyspnea), and fever. Brain abscess - location and size determine neurologic picture (a combination of current or recent pneumonia and focal CNS signs suggests Nocardia infection. Cutaneous Nocardiosis: pustules, fever, and tender lymphadenitis in the regional lymph nodes.

1. Growth on ordinary laboratory medium like BAP after 2 days.
2. Colonies initially have a dry, wrinkled, chalklike appearance, adhere to the agar, and develop white to orange pigment over time.
3. Sputum cultures or direct aspirates from skin or other purulent sites can reveal filaments of Gram-positive rods with primary and secondary branches.
4. Demonstration of acid-fastness, when combined with other observations, is diagnostic of N. asteroides or N. brasiliensis.
5. Nocardia acid-fast staining employs a decolorizing agent weaker than that used for mycobacteria (it is a weaker acid-fast organism).
6. The Nocardia are not susceptible to penicillin. The current DOC is sulfonamides. An example is trimethoprim-sulfamethoxazole.

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Authored by Mary T. Johnson, Ph.D. ©Copyright 1999-2007, Indiana University School of Medicine Last modified December 1, 2007