Actinomycetes and Nocardia

Bacteria in these genera are considered together because of several common characterisitcs. All are ubiquitous soil saprophytes that are not considered among the primary pathogenic bacteria for humans. The appearance of both organism groups with gram-staining is variable, with filaments and sometimes what is desribed as "beads on a string". The filamentous nature and colony morphology on agar makes them seem similar to fungi, but they are true bacteria. The localized infections they produce with trauma in immunocompetent individuals is similar: sinuses form spontaneously to drain the accumulated pus and secretions. There are several important characteristics for the two groups, detailed below, that are very different. Nocardiosis is much more likely to be found in immunocompromised patients, and pulmonary infection or brain abscess are two syndromes found with this disease. In addition, Nocardia is weakly acid-fast, and will take up carbol-fuchsin stain with

I. Actinomycetes sp.

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.

Image courtesy CDC Public Health Image Library, 2007
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.

II. Nocardia sp ( Nocardia asteroides and Nocardia brasiliensis)

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.

Image courtesy CDC Public Health Image Library, 2007
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. Nocardia asteroides is among the most common of the Actinomycetes that also cause bacterial mycetoma worldwide. Mycetoma is a slowly progressive, destructive infection. It cause cutaneous and subcutaneous tissue infections, associated with spontaneous eruptions that drain pus and bacteria (sinus tracts). The fascia and bone can be effected as well (see radiograph at the right).

This radiograph of a patient's right arm shows bone destruction
due to N. asteroides infection. Images (above & below)
courtesy CDC Public Health Image Library, 2007
C. IDENTIFICATION, CULTURE AND TREATMENT

Growth on ordinary laboratory medium like BAP after 2 days.

Colonies initially have a dry, wrinkled, chalklike appearance, adhere to the agar, and develop white to orange pigment over time.

Sputum cultures or direct aspirates from skin or other purulent sites can reveal filaments of Gram-positive rods with primary and secondary branches.

Demonstration of acid-fastness, when combined with other observations, is diagnostic of N. asteroides or N. brasiliensis.

Nocardia acid-fast staining employs a decolorizing agent weaker than that used for mycobacteria (it is a weaker acid-fast organism).

The Nocardia are not susceptible to penicillin. The current DOC is sulfonamides. An example is trimethoprim-sulfamethoxazole.

E-mail Dr. Johnson
johnsomt (at) iupui.edu
for comments or suggestions.

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.	Image courtesy CDC Public Health Image Library, 2007
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.	Image courtesy CDC Public Health Image Library, 2007
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. Nocardia asteroides is among the most common of the Actinomycetes that also cause bacterial mycetoma worldwide. Mycetoma is a slowly progressive, destructive infection. It cause cutaneous and subcutaneous tissue infections, associated with spontaneous eruptions that drain pus and bacteria (sinus tracts). The fascia and bone can be effected as well (see radiograph at the right).	This radiograph of a patient's right arm shows bone destruction due to N. asteroides infection. Images (above & below) courtesy CDC Public Health Image Library, 2007
C. IDENTIFICATION, CULTURE AND TREATMENT Growth on ordinary laboratory medium like BAP after 2 days. Colonies initially have a dry, wrinkled, chalklike appearance, adhere to the agar, and develop white to orange pigment over time. Sputum cultures or direct aspirates from skin or other purulent sites can reveal filaments of Gram-positive rods with primary and secondary branches. Demonstration of acid-fastness, when combined with other observations, is diagnostic of N. asteroides or N. brasiliensis. Nocardia acid-fast staining employs a decolorizing agent weaker than that used for mycobacteria (it is a weaker acid-fast organism). The Nocardia are not susceptible to penicillin. The current DOC is sulfonamides. An example is trimethoprim-sulfamethoxazole.