Actinomycetes and propionibacterium
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Actinomycetes and Propionibacterium. (Those that form filaments). Actinomycetes. Classification Order – Actinomycetales Show fungus-like characteristics such as branching in tissues or in culture (look like mycelia).

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Actinomycetes and propionibacterium

Actinomycetes and Propionibacterium

(Those that form filaments)


  • Classification

    • Order – Actinomycetales

      • Show fungus-like characteristics such as branching in tissues or in culture (look like mycelia).

        • The filaments frequently segment during growth to produce pleomorphic, diphtheroidal, or club shaped cells.

      • The cell wall and the internal structures are typical of bacteria rather than fungi.

      • Some are aerobic and others are anaerobic.

      • All are slow growing


  • The anaerobic genera: Actinomyces, Arachnia, and Bifidobacterium

    • Morphology and cultural characteristics

      • G+ branching, or diphtheroid-like bacilli

      • Anaerobic and require CO2 for growth

      • Non-sporing

      • Will grow on anaerobic BA or PEA.

        • A. israelii, the most commonly isolated species, produces rough, granular colonies that resemble molars.

    • Biochemistry

      • ID by gas liquid chromatography (GLC) of metabolic by-products or fluorescent antibody studies


  • Clinical significance

    • Are part of the NF found in the cavities of humans and other animals.

    • All may cause actinomycosis or “lumpy jaw” which is a cervicofacial infection that used to occur following tooth extractions or dental surgery which provided traumatized tissue for growth of the microorganism which may also invade the bone.

      • This is rare today because of prophylactic antibiotic therapy.

    • May cause thoracic or abdominal infections

    • May cause meningitis, endocarditis, or genital infections


  • Every kind of infection is characterized by draining sinuses, usually containing characteristic granules which are colonies of bacteria that look like dense rosettes of club-shaped filaments in radial arrangement

  • Treatment

    • Penicillin

  • Actinomycetes4

    • The aerobic genera: Nocardia, Actinomadura, and Streptomyces. There are three clinically important species of Nocardia – N. asteroides, N. brasilensis, and N. caviae

      • Morphology and cultural characteristics

        • G+ branching bacillus that may fragment to bacillary or coccoid forms

        • Aerobic

        • Specimens should be inoculated onto 7H10 agar or Lowenstein-Jensen agar and brain heart infusion agar.

          • Colonies produced are typically orange, dry, crumbly, and adherent.

        • The organisms are weakly acid fast or non acid fast


    • Biochemistry

      • The organisms are identified based on sugar fermentations and hydrolysis reactions (caseine, tyrosine, etc.)

    • Clinical significance

      • Mycetoma – organism enters the body through breaks in the skin and causes a localized infection involving skin, cutaneous, and subcutaneous tissue.

        • The three most characteristic features seen are swelling, draining sinuses and granules.

        • This disease can also be caused by fungi as well as Nocardia, Actinomadura, and Streptomyces.


    • Nocardiosis – is a localized or disseminated disease occurring after inhalation of organisms.

      • Pulmonary infections resemble tuberculosis and can remain confined to the lungs or may disseminate, with a predilection for the brain and meninges.

      • The disease is characterized by multiple confluent abscesses and intense suppuration.

      • It is usually a disease of compromised hosts.

  • Antimicrobic susceptibility/treatment

    • Mycetoma – aminoglycosides

    • Nocardiosis – sulfonamides or sxt

  • Propionibacterium

    • Classification

      • Two species P. acnes and P. granulosum.

      • Are described as anaerobic diphtheroids, though some can grow in CO2.

      • Most clinical isolates are P. acnes which is part of the NF of skin.

    • Morphology and cultural characteristics

      • Pleomorphic, small G+B, may have Chinese letter configurations or may be branching.


    • Grow well on CBA, producing tiny translucent to opaque and white to gray colonies.

    • Growth may be slow.

    • Anaerobic, though occasional strains of P. granulosum grow in CO2

  • Biochemistry

    • Catalase +

    • Indole +/-

    • Ferment glucose

    • Produce caseinase

  • Propionibacterium3

    • Virulance factors

      • Protease

    • Clinical significance –

      • Is part of skin NF

      • Has been implicated in causing acne –

        • During adolescence more sebum is produced, and P. acnes metabolizes it to produce fatty acids.

        • These may contribute to the inflammatory response seen in acne.

      • Has also been isolated from joint infections


    • Antibiotic susceptibility/treatment

      • Tetracycline

      • Acutane – inhibits sebum formation and is only used in severe cases of acne because there are many side effects.