Actinobacillus species

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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
  • myositis and 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
  • Causes pneumonia in pigs
  • 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