Variation in M protein production among Streptococcus pyogenes strains according to emm genotype

Abstract

M protein is an important virulence determinant in Streptococcus pyogenes, but the amounts of M protein in various strains of the species remain to be elucidated. To assess the amount of M protein in strains of each emm genotype, dot blot analysis was performed on 141 clinically isolated strains. Among the cell membrane-associated proteins, M protein was present in greater quantities in the emm1, 3, and 6 strains than in the other emm strains. In addition three strains, one each of the emm1, 3, and 6 types, showed prolific M protein production (M protein-high producers). These three emm genotypes are frequently isolated in clinical practice. Sequencing of the csrRS gene, one of the two-component signal transduction systems implicated in virulence, was performed on 25 strains bearing different amounts of M protein. CsrS mutations, in contrast to CsrR protein, were detected in 11 strains. The M protein-high producer strain of emm1 type carried two amino acid substitutions, whereas the other three emm1 strains carried only one substitution each. The M protein-high producer expressed its emm gene more strongly than the corresponding M protein-low producer did according to TaqMan RT-PCR. These observations suggest that the accumulation of amino acid substitutions in CsrS protein may contribute, at least in part, to the large amount of M protein production seen in several emm genotypes. Key words emm genotype, M protein, Streptococcus pyogenesStreptococcus pyogenes is an important human pathogen with several different clinical manifestations. Pharyngitis among school-age children is one of the most common conditions caused by S. pyogenes. In addition, S. pyogenes has been responsible for severe invasive diseases such as sepsis and STSS throughout the world, particularly during the last 20 years (1).Streptococcus pyogenes produces a virulence determinant, known as M protein, which occurs on the cell surface and has a dimeric alpha-helical coiled-coil structure. List of Abbreviations:ANOVA, one-way analysis of variance; AP, alkaline phosphatase; BHIY brain-heart infusion with 0.3% yeast extract; cDNA, complementary DNA; Ct, ritical threshold cycle; OD, optical density; SpeB, streptococcal pyrogenic exotoxin B; S. pyogenes, Streptococcus pyogenes; STSS, streptococcal toxic shock syndrome; TTBS, tris-buffered saline with 0.05% Tween-20, pH 7.5; WT, wild type.Since identification of the species by Rebecca Lancefield, this protein has possibly been one of the best-studied molecules among the known streptococcal virulence determinants. Over the last few decades, possible roles suggested for M protein in streptococcal infection have included: (i) effecting an antiphagocytic function against human neutrophils (2, 3); (ii) promoting adhesion to, and invasion into, epithelial cells (4); (iii) enabling size variation of the N-terminal region for the purpose of escaping recognition by human antibodies (5, 6); and (iv)forming,