Actinobacillus species

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• Cause peritonitis in horses
• A. pleuropneumoniae causes pneumonia in pigs
• Cause granulomatous inflammation.
  • E.g. Actinobacillus lignieresii causes wooden tongue in cattle -> myositis
• A. equuli in arthritis of horses

Actinobacillus characteristics

• Small Gram negative coccobacilli
• Oxidase negative
• Do not grow on MacConkey

Actinobacillus lignieresii

• Commensal in the mouth of sheep and cattle
• Penetrates damaged mucosa to cause a granuloma, a condition known as Actinobacillosis
• Enodogenous, sporadic and chronic infection
• Lesions in the tongue, cheek, lips and sometimes in the lower gut and lungs from aspiration
• Often spreads from the site of infection to lymphatics
• Formation of fibrous tissue in the lesions lead to hardening of the tissue, hence the condition is known as 'wooden tongue' in cattle
• In sheep abscesses with thick walls are produced
• Feeding is impaired, causing loss of condition
• Recovery with antibiotics

Actinobacillus equuli

• Commensal of the equine intestinal mucosa
• Infection at birth causes severe enteritis and septicaemia within 24 hours, known as sleepy foal disease
• In foals that survive neonatal infection the condition progresses to cause joint infections and purulent nephritis
• RTX group cytotoxin present

Actinobacillus suis

• Fatal septicaemia in pigs 1-8 weeks old
• Causes abscesses in joints and lungs of older pigs
• Carried in the nasopharynx of pigs and nose of horses
• Carriage may confer immunity to the more severe pleuropneumonia

Actinobacillus pleuropneumoniae

• Contagious porcine pleuropneumonia
• Endemic in UK
• Most strains are NAD-dependent (grow on Heated Blood agar)
• Positive CAMP reaction
• 12 serotypes causing the same disease
• Different serotypes in different regions, with serotypes 3,6 and 8 the most common in the UK