Objective—To develop polymerase chain reaction-restriction
fragment length polymorphism (PCR-RFLP)
analysis for molecular typing of strains of
Streptococcus zooepidemicus and to use the new
typing method to analyze a collection of isolates from
the respiratory tract of Thoroughbreds.
Sample Population—10 strains of S zooepidemicus,
65 isolates from the respiratory tract of 9 yearlings
following long distance transportation, and 89 isolates
from tracheal aspirates of 20 foals with pneumonia.
Procedure—Phenotypic variations in the SzP protein
were detected by western immunoblot analysis.
Using PCR-RFLP analysis, genotypes were obtained
with primer sets from the SzP gene, followed by
restriction endonuclease digestion of the amplicons.
Results—Unique genotypic patterns were obtained
with a primer set designed from both ends of the
structural gene and the restriction endonuclease Dde
I. Forty-five isolates from the lymphoid tissue within
the pharyngeal recess (ie, pharyngeal tonsil) of yearlings
included 10 SzP genotypes and SzP phenotypes.
Isolates from the trachea of each yearling were of a
single genotype that was also present among isolates
from the pharyngeal tonsil of the same horses.
Isolates from tracheal aspirates of foals belonged to
Conclusion and Clinical Relevance—Analysis of the
SzP gene by use of PCR-RFLP was effective for molecular
typing of strains of S zooepidemicus in the study of
respiratory tract disease in horses. Results of PCR-RFLP
analysis indicate that a single strain of S zooepidemicus
can migrate from the pharyngeal tonsil to the trachea at
a high rate in horses undergoing long distance transportation.
(Am J Vet Res 2002;63:1298–1301)
Objective—To develop a method for typing
Streptococcus equi on the basis of the DNA
sequence of the genes that produce an M-like protein
and to compare isolates among the United States,
Japan, and other countries.
Sample Population—S equi strains CF32, Hidaka/95/2,
and NCTC9682 as well as 82 other isolates from the
United States, Japan, and other countries obtained during
1975 to 2001.
Procedure—DNA sequences of the structural genes
( SeM and SzPSe) that produce M-like proteins were
determined for 3 representative strains to find a variable
region. Variability in this region of SeM was then
determined for the other isolates. Amino acid
sequences were deduced and analyzed phylogenetically
by use of the neighbor-joining method.
Results—Sequence diversity was detected in the
N-terminal region of SeM but not in SzPSe of the 3
representative strains. Base substitutions in the
variable region of SeM varied in a nonsynonymous
manner, resulting in variation in the amino acid
sequence. Eighty-five isolates were categorized as
32 types of SeM on the basis of differences in the
deduced amino acid sequences.
Conclusions and Clinical Relevance—This study
documented a region in the N-terminal portion of
SeM that varies in a nonsynonymous manner. This
information should be useful in molecular epidemiologic
studies of S equi. (Am J Vet Res 2005;