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

Overview

• Mainly pathogens of farm animals
• Commensals of mucosa of upper respiratory tract and oral cavity
• Cannot survive long in the environment, therefore carrier animals are important in their transmission

Actinobacillus characteristics

• Small Gram negative coccobacilli
• Oxidase negative
• Do not grow on MacConkey
• Non-motile
• Facultative anaerobes which ferment carbohydrates to produce acid

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
• A. equuli in arthritis of horses
• 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
• Acute disease in susceptible herds with high morbidity and mortality
• Carrier herds have some immunity, protecting from acute disease, where lesions are often subclinical, and deaths sporadic
• Lung scarring and pleural adhesions in many recovered animals
• Solid immunity develops in recovered animals to all serotypes
• The disease is spread between herds by carrier pigs
• The bacteria on the palatine tonsil are undetected by serologucal tests and swabbing, and can therefore cause an outbreak in naive pigs
• Killed and bacterin vaccines are available
• Produce one or two RTX group cytolytic toxins
• RTX toxins:
  • 'Repeat in ToXin' - named because there are several peptide repeats within the molecules
  • Produced by various Gram-negative bacteria
  • Possess four contiguous genes, A, B, C and D
  • A is the structural gene; B and D are required for secretion; C allows post-translational activation of the gene product of A into a functional product
  • ApxI is a strong haemolysin with cytolytic activity
  • ApxII is a weak haemolysin
  • ApxIII is a cytotoxin
  • Different Actinobacillus pleuropneumonia serotypes secrete a particular combination of toxins; American serotypes secrete ApxI and II; European serotypes secrete ApxII and III