Actinomycetes

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• Cause peritonitis in dogs and peritonitis in cattle and peritonitis in pigs
• Micropolyspora faeni and Thermactinomyces vulgaris in Bovine Farmers Lung
• Thermactinomyces vulgaris may cause COPD

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:
  • Penicillin or broad spectrum antibiotics
  • Unclassified Actinomyces species isolated from closed cases of Poll Evil and Fistulous Withers

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