Category:Actinomycetes

Overview

• Gram positive bacteria
• Grow slowly on media and produce branching filaments
• Opportunistic infections causing inflammatory responses and granulomatous reactions
• Animal pathogens include Actinomyces, Arcanobacterium, Actinobaculum, Nocardia and Dermatophilus

Arcanobacterium, Actinomyces and Actinobaculum species

• Non-motile, non-spore-forming bacteria
• Anaerobic or facultative anaerobes
• Grow on enriched media; non-acid fast
• Colonise mucous membranes
• Modified Ziehl-Neelson negative

<ncl style=compact maxdepth=2 headings=bullet headstart=2 showcats=1 showarts=1>Category:Actinomycetes</ncl> Arcanobacterium pyogenes

Actinomyces

Actinobaculum suis

Nocardia

• Facultative intracellular bacterium
• Aerobic short branching rods
• Non-motile
• Spores from aerial filaments when cultured
• Grow on Sabouraud dextrose agar
• Cell wall contains mycolic acids (hence slightly acid fast)
• Nocardia asteroides
  • Found in soil and decaying vegetation - saprophytic
  • Opportunistic infection of immunocompromised animals
  • Infection via inhalation, wounds or teat canal; also ingestion
  • Causes granulomatous lesions in animals
  • Canine nocardiosis:
    • Thoracic, cutaneous and disseminated forms
    • Cutaneous pyogranulomas: ulcers or granulomatous swellings with discharging fistulae
    • peritonitis
    • pleuritis and pyothorax with fever, anorexia and respiratory distress
    • Disseminated lesions
    • Treat with appropriate systemic antibiotics for 6 weeks
  • Cattle: chronic mastitis; abortion
  • Pigs: abortion
  • Sheep, goats, horses: wound infections; mastitis; pneumonia
  • Survives and multiplies in macrophages
  • Superoxide dismutase and catalase as well as a thick peptidoglycan wall prevent activity of phagocytes
  • Chronic, progressive disease
  • Positive modified Ziehl-Neelson
  • Culture on blood agar and incubate under aerobic conditions at 37 degrees centigrade for 10 days
  • White, powdery colonies, adherent to the agar appear after 5 days
  • Subculture onto Sabouraud dextrose agar yields wrinkled, orange colonies
  • Lesions difficult to treat due to resistance of organisms to many antimicrobials (e.g. penicillins)
  • Cell-mediated immunity required
• Nocardia farcinica causes bovine farcy, a chronic infection of superficial lymphatic vessels and lymph nodes

Dermatophilus congolensis

• Filamentous, branching actinomycete
• Aerobic
• Produces motile zoospores
• No growth on Sabouraud dextrose agar
• Dermatophilosis most prevalent in tropical and subtropical regions
• Organisms found in scabs and in foci in skin of carrier animals
• Dormant zoospores become activated when moisture and temperature levels are favourable
• Zoospores may survive 3 years in scabs
• Pathogenicity:
  • Does not usually invade healthy skin
  • Entrance after trauma or persistent wetting
  • Activated zoospores produce germ tubes which develop into filaments which invade the epidermis
  • Invasion causes an accute inflammatory response with many neutrophils
  • Microabscesses are formed in the skin
  • Raised crusts develop in the affected regions
• Pathology
• Diagnosis:
  • Giemsa-stained smears from scabs reveal branching filaments containing zoospores
  • Immunofluorescence
  • Scab material can be cultured on blood agar at 37 degrees centigrade, 2.5-10% carbon dioxide for 5 days
  • Zoospores can be cultured
  • After incubation, colonies are yellow and haemolytic (after 48 hours); they later become rough and yellow, and gain a mucoid appearance
  • No growth on Sabouraud dectrose agar
• Clinical infections:
  • Infection usually confined to epidermis
  • Dermatophilosis
  • Disease most prevalent in young animals
  • Damage to the skin predisposes to infection; blood-sucking insects also thought to be involved in transmission
  • Lesions after heavy rainfall predominantly affect dorsum of farm animals
  • Papules, serous, exudative matting of hair, raised crusty scabs
  • Scab formation more prominent in sheep and cattle than in horses
  • Lesions may resolve within weeks if dry weather, or may progress
• Treatment:
  • Parenteral antibiotics e.g oxytetracycline, pr penicillin-streptomycin combinations

• Micropolyspora faeni and Thermactinomyces vulgaris in Bovine Farmers Lung
• Thermactinomyces vulgaris may cause COPD