Characterization of group A streptococcal strains Sv and Su: determination of emm gene typing and presence of small vir regulon.
The emm gene typing of GAS (group A streptococcus) strains Sv and Su and the molecular structure of the vir regulon were decided. An emm(-like) gene from the chromosomal DNA of GAS strain Sv was amplified with forward and reverse primers, which were selected from the best conserved portion in leader sequences of different strains and the C-terminal conserved portion, respectively, for determination of the M protein gene type. Strain Sv was defined as serotype M23, because deduced N-terminal amino acid positions of the products are identical to those of the M type 23 (emml) gene derived from GAS strain M23-MEMPHIS (M serotype 23, GenBank accession number U11953). When the vir regulon of strain Sv was examined by polymerase chain reaction mapping and compared with that of GAS strain Su, they had a similar size in length. In addition, when sequencing analysis of the DNA fragment of 4791 base pairs (bp) encoding three open reading frames (orf, mga, and emm) and the upstream region of scpA from genomic DNAs of both strains was performed, the sequence of the DNA from strain Sv was, except for 1 bp (T for C at position 4124), identical to that of the DNA from strain Su. These data show that both strains possess the genes in the order of mga (virR or mry) -emm -scpA designated as the small vir regulon. The effect of the formation of alternative pathway C3 convertase of complement on the GAS strains Sv and Su was also examined. When GAS strains Sv and Su were incubated in NHS containing radiolabeled C3 in the presence of Mg-EGTA, binding of C3 to Su bacteria was dose-dependent, whereas less binding of C3 to Sv bacteria was seen. Taken together, the data suggest that M protein could be expressed on the surface of the Sv bacteria, but not on the Su bacteria.