Comparison of the phenotypes of Streptococcus zooepidemicus isolated from tonsils of healthy horses and specimens obtained from foals and donkeys with pneumonia.

The research study investigates whether the strains of Streptococcus zooepidemicus that cause pneumonia in foals and donkeys are similar to those found in the tonsils of healthy horses. The study found that despite the diversity in genotype and phenotype, pneumonia-causing strains with phenotypes similar to those in healthy horses’ tonsils were also found.

Methods used in study

• Five tonsil specimens from healthy horses, eight tracheal washes and six lung specimens from foals with pneumonia, and five nasopharyngeal swab specimens from donkeys with bronchopneumonia were collected.
• The M-like SzP proteins from five samples of S. zooepidemicus from the tonsils and clinical specimens were compared using immunoblots.
• The SzP gene of thirteen isolates from a health horse and nine horses and donkeys with pneumonia were sequenced and compared.
• Measurements were taken of cell-associated hyaluronic acid concentration and resistance to phagocytosis.

Findings of the study

• Multiple SzP phenotypes similar to those found in foals or donkeys with pneumonia were found in the tonsils of each healthy horse.
• Horses and donkeys with pneumonia were infected with a single strain that had the same SzP phenotype.
• Immunoblot phenotype differences were associated with sequence differences, and several SzP genotypes were found in both healthy horses and those with pneumonia.
• Isolates with high concentrations of cell-associated hyaluronic acid were found to be more resistant to phagocytosis.

Conclusions of the study

• An SzP-specific immunoblot is effective in measuring diversity among strains of S. zooepidemicus.
• Pneumonia was found to be caused by single strains with SzP phenotypes similar to those found in tonsils of healthy horses.
• Despite the diversity of SzP phenotype and genotype among isolates from animals with pneumonia, SzP phenotype was not an important determinant of invasiveness or epizootic capabilities.