Difference between revisions of "Actinomycetes"

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===''Nocardia''===
 
===''Nocardia''===
  
 +
*Facultative intracellular bacterium
 
*Aerobic short branching rods
 
*Aerobic short branching rods
 
*Non-motile
 
*Non-motile
*Spores from aerial filaments
+
*Spores from aerial filaments when cultured
 
*Grow on Sabouraud dextrose agar
 
*Grow on Sabouraud dextrose agar
 
*Cell wall contains mycolic acids (hence slightly acid fast)
 
*Cell wall contains mycolic acids (hence slightly acid fast)
*''Nocardia asteroides'' found in soil
+
*''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
 
*Causes granulomatous lesions in animals
*Involved in [[Peritoneal cavity - inflammatory#In dogs|peritonitis]] and [[Bacterial infections#Nocardiosis|pleuritis]] in dogs
+
*Canine nocardiosis: cutaneous pyogranulomas; [[Peritoneal cavity - inflammatory#In dogs|peritonitis]]; [[Bacterial infections#Nocardiosis|pleuritis]] and pyothorax; disseminated lesions
 +
*Cattle: chronic mastitis; abortion
 +
*Pigs: abortion
 +
*Sheep, goats, horses: wound infections; mastitis; pneumonia
 
*Survives and multiplies in macrophages
 
*Survives and multiplies in macrophages
*Lesions in thoracic cavity, skin and other tissues
+
*Superoxide dismutase and catalase as well as a thick peptidoglycan wall prevent activity of phagocytes
 
*Chronic, progressive disease
 
*Chronic, progressive disease
 
*Lesions difficult to treat due to resistance of organisms to many antimicrobials (e.g. penicillins)
 
*Lesions difficult to treat due to resistance of organisms to many antimicrobials (e.g. penicillins)
 +
*Cell-mediated immunity required
 +
*''Nocardia farcinica'' causes bovine farcy
  
  

Revision as of 16:21, 17 February 2008

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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


Arcanobacterium pyogenes

  • Characteristics:
    • Formerly known as Actinomyces pyogenes and Corynebacterium pyogenes
    • Small facultatively anaerobic rod
    • Grows slowly on blood agar to produce small, white colonies surrounded by a zone of beta-haemolysis after 48 hours
    • Produces hazy haemolysis after 24 hours; pin-point colonies after 48 hours
    • Coryneform morphology, like Chinese characters; may be curved with slightly swollen ends
    • Found in nasopharyngeal mucosa and genital tract of cattle, sheep, pigs
  • Pathogenicity
    • Opportunistic infections following injury or viral/mycoplasma infection in ruminants and pigs
    • Extracellular toxins including haemolysin, proteases, DNase and neurominidase
    • Haemolytic toxin, pyolysin, member of the thiol-activated cytolysins (pore-forming toxins); possibly cytotoxic to phagocytic cells; dermonecrotising activity
  • Clinical infections:
    • Suppurative infections
    • Abscesses especially in liver
    • Lymphadenitis, osteomyelitis, peritonitis and neural abscessation
    • Pyometra
    • Endometritis
    • Summer mastitis
    • Ovine foot disease
    • Arthritis
    • Umbilical infections
    • Suppurative pneumonia
  • Treatment:


Actinomyces

  • Usually long filamentous branching Gram positive rods
  • Anaerobic or facultativlyy anaerobic and capnophilic
  • Live in nasopharyngeal and oral mucosa
  • Cause pyogranulomatous lesions
    • Actinomyces bovis
      • Found naturally in oral cavity of cattle
      • Prefers anaerobic conditions but not strict anaerobe
      • Entry of organism into tissues following trauma to the mucosa from rough feed or tooth eruption
      • Causes granulomatous inflammation of soft tissues and bone, causing lumpy jaw
      • Usually invades mandible to cause osteomyelitis and may extend to surrounding muscles
      • The lesions begins as a painless swelling of the affected bone
      • Swelling becomes more painful and enlarges over a number of weeks, gaining fistulous tracts which discharge pus
      • Organisms found in yellow sulphur granules
      • Club colony formation
      • Colonies adhere to agar media and are non-haemoltic
      • Surgical treatment possible when lesions are small
      • Prolonged parenteral penicillin treatment may be beneficial early in the disease
    • Actinomyces viscosus
      • Commensal of oral cavity of dogs and humans
      • Canine actinomycosis
      • Causes localised subcutaneous pyogranulomatous lesions and fibrovascular proliferation of peritoneal and pleural surfaces in dogs
      • Leads to pyothorax
      • Respiratory distress
      • Cutaneous pustules in horses
      • Abortion in cattle
      • Rods contained in soft grey granules which release the organism when squashed
      • Two types of colonies: large and smooth colonies with V, Y and T configurations or small and rough colonies with short branching filaments
      • Grow in 10% carbon dioxide
      • Usually responds to penicillin
    • Actinomyces hordeovulneris
      • Organism found in seed heads of certain grasses
      • Colonies adhere to agar and are non-haemolytic
      • Filamentous, branching organisms
      • Cause cutaneous and visceral abscessation, pleuritis, peritonitis and arthritis in dogs


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: cutaneous pyogranulomas; peritonitis; pleuritis and pyothorax; disseminated lesions
  • 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
  • Lesions difficult to treat due to resistance of organisms to many antimicrobials (e.g. penicillins)
  • Cell-mediated immunity required
  • Nocardia farcinica causes bovine farcy


Dermatophilus congolensis

  • Aerobic
  • Motile zoospores
  • No growth on Sabouraud dextrose agar
  • Found in scabs and in foci on skin of carrier animals