Actinomycetes

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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:
      • 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 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