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
- 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

Micropolyspora faeni and Thermactinomyces vulgaris in Bovine Farmers Lung
Thermactinomyces vulgaris may cause COPD