Comparison of the phenotypes of Streptococcus zooepidemicus isolated from tonsils of healthy houses and specimens

Objective-To determine whether streptococcal pneumonia is caused by strains of Streptococcus zooepidemicus similar to those obtained from the tonsils of healthy horses. Sample Population-5 tonsils from healthy horses, 8 tracheal washes and 6 lu ng specimens from foals with pneumonia, and 5 nasopharyngeal swab specimens from donkeys with acute bronchopneumonia. Procedure-Variable M-like protectively immunogenic SzP proteins of 5 isolat es of S zooepidemicus from each tonsil and clinical specimen were compared, using immunoblots. The SzP gene of 13 isolates representative of various S zP immunoblot phenotypes from 1 healthy horse and 9 horses and donkeys with pneumonia were sequenced and compared. Cell-associated hyaluronic acid con centration and resistance to phagocytosis of some isolates were measured. Results-Tonsils of each healthy horse were colonized by several SzP phenoty pes similar to those of foals or donkeys with pneumonia. in contrast, multi ple isolates from animals with pneumonia had the same SzP phenotype, indica ting infection by a single strain or clone. Analysis of the SzP sequence co nfirmed that differences in immunoblot phenotype were associated with seque nce differences and that several SzP genotypes were in healthy horses and a nimals with pneumonia. Isolates with high concentrations of cell-associated hyaluronic acid were more resistant to phagocytosis. Conclusions and Clinical Relevance-An SzP-specific immunoblot is a useful, sensitive measure of diversity among strains of S zooepidemicus. Single str ains with SzP phenotypes similar to those found in tonsils of healthy horse s cause pneumonia. Because of the diversity of SzP phenotype and genotype a mong isolates from animals with pneumonia, SzP phenotype is not an importan t determinant of invasiveness or epizootic capabilities.