Comparison of the phenotypes of Streptococcus zooepidemicus isolated from tonsils of healthy horses and specimens obtained from foals and donkeys with pneumonia.
OBJECTIVE
To determine whether streptococcal pneumonia is caused by strains of Streptococcus zooepidemicus similar to those obtained from the tonsils of healthy horses.


METHODS
5 tonsils from healthy horses, 8 tracheal washes and 6 lung specimens from foals with pneumonia, and 5 nasopharyngeal swab specimens from donkeys with acute bronchopneumonia.


METHODS
Variable M-like protectively immunogenic SzP proteins of 5 isolates of S. zooepidemicus from each tonsil and clinical specimen were compared, using immunoblots. The SzP gene of 13 isolates representative of various SzP immunoblot phenotypes from 1 healthy horse and 9 horses and donkeys with pneumonia were sequenced and compared. Cell-associated hyaluronic acid concentration and resistance to phagocytosis of some isolates were measured.


RESULTS
Tonsils of each healthy horse were colonized by several SzP phenotypes similar to those of foals or donkeys with pneumonia. In contrast, multiple isolates from animals with pneumonia had the same SzP phenotype, indicating infection by a single strain or clone. Analysis of the SzP sequence confirmed that differences in immunoblot phenotype were associated with sequence differences and that several SzP genotypes were in healthy horses and animals with pneumonia. Isolates with high concentrations of cell-associated hyaluronic acid were more resistant to phagocytosis.


CONCLUSIONS
An SzP-specific immunoblot is a useful, sensitive measure of diversity among strains of S. zooepidemicus. Single strains with SzP phenotypes similar to those found in tonsils of healthy horses cause pneumonia. Because of the diversity of SzP phenotype and genotype among isolates from animals with pneumonia, SzP phenotype is not an important determinant of invasiveness or epizootic capabilities.
Anzai
T
T
Gluck Equine Research Center, University of Kentucky, Lexington 40546-0099, USA.
Walker
J A
JA
Blair
M B
MB
Chambers
T M
TM
Timoney
J F
JF
D000818:Animals; D017931:DNA Primers; D018397:Equidae / Q000382:microbiology*; D005798:Genes, Bacterial; D006734:Horse Diseases / Q000382:microbiology*; D006736:Horses / Q000382:microbiology*; D014066:Palatine Tonsil / Q000382:microbiology*; D010587:Phagocytosis; D010641:Phenotype; D018410:Pneumonia, Bacterial / Q000382:microbiology / Q000662:veterinary*; D016133:Polymerase Chain Reaction; D012016:Reference Values; D013290:Streptococcal Infections / Q000382:microbiology / Q000662:veterinary*; D018502:Streptococcus equi / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification
D017931:DNA Primers