Difference between revisions of "Category:Actinomycetes"

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''[[Arcanobacterium pyogenes]]''
 
''[[Arcanobacterium pyogenes]]''
  

Revision as of 12:09, 10 May 2010

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

Actinomyces


Actinobaculum suis

  • Found in preputial mucosa of healthy boars
  • Anaerobic
  • Coryneform morphology
  • Produces urease
  • 3mm diameter colonies with shiny raised centre and dull edge
  • Disease transmitted at coitus
  • Sows develop disease within 3-4 weeks of mating
  • Produces lesions in urinary tract of sows
  • Cystitis and pyelonephritis in sows
  • Anoreixa, arching of back, dysuria and haematuria
  • May be fatal


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


Subcategories

This category has the following 2 subcategories, out of 2 total.

A

N

Pages in category "Actinomycetes"

The following 5 pages are in this category, out of 5 total.