Actinomycetes

• What type of bacteria are Actinomycetes?

  Gram-positive filamentous bacilli
• What are the general characteristics of Actinomycetes?

  They are non-motile, non-capsulated, mostly aerobic, and catalase-positive.
• What is the primary ecological role of Actinomycetes?

  They are mostly soil saprophytes.
• In which patients may Actinomycetes cause disease?

  Particularly in immunocompromised patients.
• What is the primary source of most antibiotics?

  Actinomycetes
• Name the three major medically important genera of Actinomycetes.

  Actinomyces, Nocardia, and Streptomyces.
• What are the characteristics of Actinomyces?

  They are fastidious, slowly growing, non-sporing, anaerobic, and non-acid-fast bacteria.
• How does Actinomyces cause disease?

  They have a low virulence potential and cause disease when normal mucosal barriers are disrupted.
• Which species of Actinomyces is most commonly infecting humans?

  Actinomyces israelii
• Where is Actinomycosis more common?

  In rural areas and among agricultural workers.
• What are the forms of human actinomycosis?

  • Cervicofacial: Most common type, occurs in cheek and submaxillary regions.
  • Thoracic: Begins in the lung, often due to aspiration.
  • Abdominal: Results from spillage of intestinal flora.
  • Pelvic: Occurs in women with plastic intrauterine devices.
  • Punch actinomycosis: Rare infection of the hand.
• What is a characteristic feature of Actinomycosis (Mycetoma)?

  It is characterized by multiple granulomatous lesions that form abscesses connected by sinus tracts.
• What are sulfur granules in Actinomycosis?

  They are masses of filamentous organisms bound together by calcium phosphate.
• How long can Actinomycosis disease continue?

  It may continue for 40-50 years.
• What is the most common type of actinomycosis?

  Cervicofacial actinomycosis
• What is the laboratory diagnosis procedure for Actinomycosis?

  Specimens are collected depending on the site of infection, and sulfur granules may be demonstrated in pus.
• How are sulfur granules demonstrated in the laboratory?


  By shaking pus in a test tube with normal saline and staining the granules.
• What does Gram staining reveal in Actinomyces diagnosis?

  Thin, gram-positive, branching rods can be seen along the periphery of the granules.
• What is the culture method for Actinomyces?

  Specimens are inoculated into blood agar and incubated anaerobically at 35–37°C for up to 14 days.
• What is a characteristic colony morphology of A. israelii?

  It may form spider colonies resembling molar teeth.
• What is the appearance of Nocardia bacteria?

  Slow growing, strictly aerobic Gram-positive branching bacilli.
• What is the significance of mycolic acid in Nocardia?

  It contributes to their weakly acid-fast characteristic.
• What is the most common species of Nocardia associated with human disease?

  Nocardia brasiliensis
• What is nocardiosis?

  Opportunistic pulmonary disease in immunocompromised individuals.
• How can cutaneous Nocardia infections occur?

  Through wound contamination or trauma.
• What is the laboratory diagnosis procedure for Nocardia?

  Specimens are collected and stained with Gram and Ziehl–Neelsen stains.
• What is the culture method for Nocardia?

  Specimens are inoculated on nutrient agar and brain heart infusion agar and incubated at 36°C for 3 weeks.
• What is the appearance of Nocardia colonies on culture media?

  Colonies may appear cream, orange, or pink colored.
• What is the primary medical significance of Streptomyces species?

  They produce most of the important antibiotics.
• What is Actinomycetoma?

  A chronic destructive disease affecting the skin and underlying tissues.
• What is a characteristic feature of Actinomycetoma?

  Production of abscesses containing large compact masses of fungal hyphae known as granules.
• Where is Actinomycetoma commonly found?

  In Sudan, Somalia, North Africa, and India.
• What is the common causative organism of Madura foot?

  Actinomadura madurae
• What is the typical site affected by Madura foot?


  Feet, particularly in those who walk barefoot.
• What are the complications associated with Madura foot?

  Secondary bacterial infection and massive bone destruction.
• How does Madura foot develop?

  After trauma that introduces the infecting organism into subcutaneous tissue.
• What are the key characteristics of Streptomyces species?

  • Aerobic and non-acid-fast
  • Rarely cause actinomycetoma in humans
  • Produce important antibiotics like chloramphenicol, erythromycin, and tetracycline
  • More frequent infections in eastern India among active individuals aged 20–40 years