Actinomycetes In Soil – Nocardia

Actinomycetes Introduction

Actinomycetes are Gram-positive, filamentous bacteria. The family Actinomycetes contain three major medically important genera, Actinomyces, Nocardia, and Actinomadura. Actinomyces are anaerobic or microaerophilic and non-acid-fast, while Nocardia is acid-fast and aerobic. 

Role Of Actinomycetes In Soil

Most of the Actinomyces are soil saprophytes and others are commensals of mouths of both man and animals. The Actinomyces causes a disease known as actinomycosis. In humans, it is usually caused by Actinomycetes israelii.

Morphology Of Actinomycetes

Actinomyces is a Gram-positive, non-motile, The often grow in mycelial forms. Most non-sporing, non-acid-fast organisms. of them show tree branching. The organisms appear in the pus as granules. The sulfur granules are white pus as granules. The sulfur granule is white or yellowish in color and found only in tissues.

Culture Of Actinomycetes Bacteria

They grow best under anaerobic or microaerophilic under anaerobic actinomycetes or conditions at the optimum temperature of 37°C under 5-10% CO2. They can be grown on brain heart infusion agar, blood agar, or thioglycollate broth. On solid media, A. israelii forms spidery colonies in 48-72 hours.

Pathogenic Actinomycetes

It is a painless indurated swelling with multiple discharging sinuses. Disease caused by actinomycetes also known as actinomycosis.
Four clinical forms of Actinomycosis:

  • Cervicofacial – 70% of cases
  • Thoracic
  • Abdominal
  • Pelvic

Actinomycosis may also present as mycetoma.

  • Gingivitis
  • Periodontitis

Treatment Of Actinomycetes

Specimens Collection Of Actinomycetes

  • Pus from lesion or sinuses.
  • Discharge from fistula.
  • Sputum in pulmonary disease.
  • Tissue or biopsy.

Microscopy Of Actinomycetes

Granules are crushed between two slides and smears are prepared. One smear is stained by Gram stain and the other by acid-fast stain (decolorization with 1% sulphuric acid). Gram staining shows a dense network of thin Gram-positive filaments, surrounded by a peripheral radiating.

Gram-negative ‘clubs presenting a sun-ray appearance Acid-fast staining shows the central part as non-acid-fast surrounded by acid-fast. In the absence of sulfur granules, Gram’s staining of pus shows Gram-positive branching filaments.

Culture Of Actinomycetes israelii

The sulfur granules or pus containing Actinomycetes’ are washed and inoculated into thioglycollate broth and streaked on brain heart infusion agar (BHI agar) and blood agar. Cultures are incubated anaerobically and aerobically with 5% CO, at 37°C for at least 2 weeks.

Actinomycetes israelii produces spider colonies that resemble molar teeth. The isolate is identified by microscopy, biochemical reactions, and fluorescent antibody methods.

Treatment Of Actinomycete Bacteria

  • Surgical removal of affected tissue along with penicillin therapy is effective.

Nocardia Aerobic Actinomycete

Nocardia resembles Actinomycetes morphologically but is strictly aerobic actinomycetes. They are non-motile, Gram-positive bacteria. Aerobic Actinomycetes are acid-fast when decolorized with 1% sulphuric acid.
Species Of Nocardia

  • Nocardia asteroides
  • Nocardia brusiliensis
  • Nocardia caviae

Morphology Nocardia Aerobic 

Nocardia is Gram-positive bacteria and forms a mycelium, that fragments into rod-shaped and coccoid elements.

Culture Of Nocardia Actinomycete

Nocardia readily grows in ordinary media. They are strict aerobes. They are slow-growing (require5-14 days). They can be grown on nutrient agar Sabouraud dextrose agar (SDA) and brain heart infusion agar (BHI agar). Nocardia forms dry, granular, wrinkled colonies with pigmentation (white, yellow, pink, or red).

Infection Of Nocardia

  • Nocardia produces opportunistic pulmonary disease is known as nocardiosis in immunocompromised individuals including those with AIDS.
  • It may also cause mycetoma.

Treatment Of Nocardia


  • Pus or purulent sputum

Microscopy Of Nocardia Actinomycete

The smears are stained with Gram staining and Ziehl-Neelseen (ZN) technique using decolorization with 1% sulphuric acid. Gram-positive filamentous bacteria can be seen on Gram staining. Acid-fast bacilli are detected on the Zeihl Nielsen technique though some species are non-acid-fast.

Culture Of Nocardia Actinomycete

The specimens are inoculated on nutrient agar, Sabourad Dextrose Agar SDA, and Brain Heart Infusion BHI agar, and incubated at 36 C for 3 weeks.


Mycetoma is a localized, chronic granulomatous disease of the subcutaneous and deeper tissues affecting Commonly the foot and presenting as a tumor with multiple discharging sinuses.
This clinical syndrome was first described from Madura, India, and came to be known as Maduramycosis.

Causes of Mycetoma

Bacterial Causes
  • Actinomyces
  • Nocardia
  • Actinomadura
  • Streptomyces
Fungal causes (Mycotic Mycetoma)
  • Madurella mycetomi
  • Madurella griseus

Diagnosis Of Mycetoma

The color of granules gives some clues to the diagnosis of mycetoma. The granules are white to yellow in actinomycosis mycetoma, while in mycotic mycetomas the granules are generally black. Isolation of the organism in culture establishes the diagnosis.
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