31. nocardia, actinomyces, dermatophilus

actinomyces/nocardia gram stain

gram positive

do actinomyces and nocardia tend to cause acute or chronic infections?

chronic, slow-developing

what are the characteristics of a mycetoma?

• swelling

• draining sinuses

• granules (in draining fluid)

actinomyces/nocardia transmission

traumatic inoculation into skin or mucosa

actinomyces/nocardia pathogenesis

• injury creates niche for bacteria → multiply as filaments, resistant to phagocytosis

• swollen lesions form that may drain and contain granules (microcolonies)

actinomyces/nocardia treatment

• debride or surgically reduce lesion

• penicillins (actinomyces) or sulfa (nocardia) for dogs & cats; iodides for large animals

actinomyces source

commensal → oral and GI microbiota

is actinomyces aerobic or anaerobic?

facultative to strict anaerobes

what disease is actinomyces associated with primarily in cattle? what causes this infection?

• “lumpy jaw” → actinomyces bovis

• caused by traumatic injury within the oral cavity (ex. chewing on something sharp)

  • normal flora inoculate into soft tissue

  • anaerobic environment

chronic lumpy jaw lesions

• mycetoma

• actinomyces tends to invade bone

how is lumpy jaw treated?

• resect or drain lesions

• treat with iodides (relatively inexpensive), penicillins

• may recur

• try to get cow through pregnancy or lactation

• treatment is difficult, expensive, and prolonged

other presentations of actinomycosis

• actinomyces suis → swine; soft tissue wounds, mastitis

• dogs and cats → thoracic abscesses

• periodontal disease

  • can contribute to chronic inflammation, bone loss

nocardia sources

environmental → found in soil, water (not commensal)

is nocardia aerobic or anaerobic?

aerobic

in dogs, what type of lesion is often caused by nocardia?

• soft tissue abscesses

  • purulent, bloody “tomato soup” exudate

• can be mixed infections

nocardiosis in other species

• mastitis in cattle (uncommon)

  • usually contamination during dry cow therapy, chronic, difficult to treat

• horses → placentits

• occasional pathogen of fish, shellfish

• humans → skin infections following inoculation; if inhaled, can mimic tuberculosis (rare)

how are actinomyces and nocardia similar? how are they different?

what body site/tissue does dermatophilus infect?

invades epidermis (attracted to CO₂)

dermatophilus source

skin lesions on infected animals

how is dermatophilus transmitted?

• wet conditions enhance survival and transmission from animal to animal via sloughed skin

• short term survival on vegetation

dermatophilus pathogenesis

• motile zoospores in skin lesions swim to new sites on same or different animal

• burrow into skin → form large filaments that fragment into zoospores

• attract PMNs → skin sloughs → can transmit to others

what types of lesions do dermatophilus cause?

superficial crusty, scabby lesions

what diseases do dermatophilus cause?

• “lumpy wool disease”

• “strawberry footrot”

• “rain scald”

dermatophilus diagnosis

• appearance of lesions

• visualize organisms in scabs (Giemsa stain)

dermatophilus treatment

• improve hygiene (e.g. wet conditions)

• penicillin, other antibiotics

• topical treatment (debride lesions)

what is the significance of ticks in dermatophilus transmission?

in the tropics, amblyoma ticks serve as a mechanical vector to transmit d. conglolensis