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