Hemolysin patterns of Actinobacillus pleuropneumoniae

Area of Science:

• Veterinary Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• Actinobacillus pleuropneumoniae causes significant economic losses in swine due to pleuropneumonia.
• Hemolysins are virulence factors contributing to bacterial pathogenicity.
• Different serotypes of A. pleuropneumoniae exhibit distinct hemolytic activities.

Purpose of the Study:

• To characterize and compare the secreted hemolytic activities of various Actinobacillus pleuropneumoniae serotypes.
• To investigate the relationship between hemolysin production and serotype virulence.
• To identify and differentiate hemolysins produced by different A. pleuropneumoniae strains.

Main Methods:

• Analysis of secreted hemolytic activities from reference strains and field isolates of 12 A. pleuropneumoniae serotypes.
• Biochemical characterization of hemolysins, including Ca2+ inducibility and ion requirements.
• Immunoblot analysis using antibodies against hemolysin I (HlyI) to assess serological relationships.

Main Results:

• Serotype 1 produced a Ca2(+)-inducible hemolysin I (HlyI).
• Serotypes 2, 4, 6, 7, and 8 produced a distinct, Ca2(+)-dependent hemolysin II (HlyII), weaker than HlyI.
• Serotypes 5a, 5b, 9, 10, and 11 produced both HlyI and HlyII, with HlyI being dominant. Serotypes 3 and 12 showed very weak hemolytic activity.
• Immunoblot analysis suggested potential serological relatedness between HlyI and HlyII.
• Active HlyI production was associated with generally virulent serotypes frequently isolated from severe pleuropneumonia outbreaks.

Conclusions:

• Actinobacillus pleuropneumoniae secretes at least two distinct hemolysins, HlyI and HlyII, with differential distribution among serotypes.
• HlyI is strongly associated with virulent A. pleuropneumoniae serotypes and severe outbreaks of swine pleuropneumonia.
• Further investigation into the serological relationship and distinct roles of HlyI and HlyII in pathogenesis is warranted.