Clonal diversity in Haemophilus pleuropneumoniae.

Area of Science:

• Veterinary Microbiology
• Bacterial Genetics
• Population Genetics

Background:

• Haemophilus pleuropneumoniae causes significant economic losses in the swine industry.
• Understanding the genetic diversity of H. pleuropneumoniae is crucial for disease control and prevention strategies.
• Previous studies have suggested a clonal population structure, but comprehensive genetic analysis was lacking.

Purpose of the Study:

• To estimate the genetic diversity of Haemophilus pleuropneumoniae isolates from pigs worldwide.
• To determine the population structure and genetic relationships among different serotypes and electrophoretic types (ETs).
• To investigate the genetic basis of pathogenicity, particularly for serotype 1.

Main Methods:

• Multilocus enzyme electrophoresis was employed to assess allelic variation in structural genes.
• 135 isolates from 14 countries, representing nine serotypes, were analyzed at 15 enzyme loci.
• Outer membrane protein patterns were also characterized for comparison with genetic types.

Main Results:

• Thirty-two distinct multilocus genotypes (electrophoretic types) were identified.
• 36 unique combinations of ET and serotype were found, with identical ETs recovered globally over 20 years, supporting a clonal structure.
• While ETs generally correlated with serotype and outer membrane protein profiles, some ETs exhibited multiple serotypes or protein patterns.

Conclusions:

• The population structure of Haemophilus pleuropneumoniae is predominantly clonal.
• Genetic diversity within serotypes constitutes a significant portion of the species' overall genetic diversity.
• Highly pathogenic serotype 1 isolates are associated with specific, closely related clones, distinct from other serotypes.