Arcanobacter 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