M-PROTEINS OF GROUP-C STREPTOCOCCI ISOLATED FROM PATIENTS WITH ACUTE PHARYNGITIS

We studied 15 strains of group C streptococci (Streptococcus equisimil is) isolated from the throats of college students with acute pharyngit is and 5 strains isolated from patients with noninfectious problems. N ineteen of the 20 strains resisted phagocytic killing during incubatio n in normal human blood, suggesting that they might express M proteins , Genomic DNA from all 20 strains hybridized with a probe correspondin g to the carboxyterminal one-third of the group A M-protein gene emm24 , a region that is highly conserved among M proteins of group A and gr oup G streptococci, The DNA sequences of the N-terminal (variable) reg ions of the M-protein-encoding genes from two disease-associated group C isolates and one control isolate were determined, The predicted ami no acid sequences of the two pharyngitis strains were identical and we re 88% homologous to the amino acid sequence of a group G M-protein ge ne. The predicted terminal amino acid sequence of the control strain d oes not correspond to any such sequences in the GenBank database, All three strains studied possess the conserved region domain common to cl ass I group A hi-protein types epidemiologically associated with rheum atic fever. These studies demonstrate the presence of M proteins in st rains of S. equisimilis isolated in cases of endemically occurring acu te pharyngitis. Certain of these proteins are similar to those of grou p G streptococci, while others may represent new M types, The similari ty in structure and function between M proteins of nonrheumatogenic se rogroups and those of rheumatogenic group A streptococci suggests that factors other than or in addition to M protein per se are likely invo lved in the pathogenesis of rheumatic fever.