Actinobacillus pleuropneumoniae

Contagious Porcine Pleuropneumonia especially of pigs under 6 months
Endemic in UK
12 serotypes causing the same disease
Different serotypes in different regions, with serotypes 3,6 and 8 the most common in the UK
Pathogenesis and pathogenicity:
- Virulent strains possess capsules which are antiphagocytic and immunogenic
- Fimbriae allow the bacteria to attach to cells of the respiratory tract
- Damaged neutrophils in the lungs produce lytic enzymes
- The sustained inflammatory response causes tissue necrosis
- Lungs consolidated and necrotic with fibrinous pleuisy at post mortem
- Produce three cytotoxins which belong to the repeats-in-structural-toxin (RTX) cytolysin family
- RTX toxins:
  - 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
  - Toxins introduce pores into cell membranes

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