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 of sheep post-dipping; arthritis in pigs and arthritis in cattle
  • Umbilical infections
  • Acute exudative pneumonia and contributes to Enzootic pneumonia of calves
  • May cause myositis
  • Unclassified Actinomyces species isolated from closed cases of Poll Evil and Fistulous Withers
• Treatment:
  • Penicillin or broad spectrum antibiotics

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 (peritonitis) 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
  • 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

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