Variation in the N-terminal region of an M-like protein of Streptococcus equi and evaluation of its potential as a tool in epidemiologic studies.

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.