actinomycetes and propionibacterium n.
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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
  • 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
  • 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
  • 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.