title: M proteins of group G streptococci isolated from bacteremic human infections.
abstract: We studied seven strains of group G streptococci isolated from clinically severe bacteremic infections in six intravenous drug abusers. These group G strains multiplied luxuriantly in fresh human blood. On electron microscopy, they exhibited surface fibrillae similar to those observed in M-protein-rich group A streptococci, but they were not serologically M typable with a battery of 39 M antisera. Rabbit antisera raised against two of the group G strains (1618 and 1750) opsonized the homologous but not the heterologous isolates and exhibited type-specific Ouchterlony immunoprecipitin reactions. Moreover, antisera raised against peptic extracts of strain 1750 also promoted phagocytic killing of that strain. Anti-1750 reacted in high titer in an enzyme-linked immunosorbent assay against peptic extracts of the homologous strain; these antibodies were removed by absorption with 1750 cells but not by absorption with heterologous strains. These studies represent, to our knowledge, the first analysis of virulence factors of group G streptococci isolated from invasive human disease. The seven epidemiologically related blood isolates of group G streptococci possess distinct type-specific, antiphagocytic surface virulence factors analogous to the M proteins of group A streptococci.
mesh_terms: D000907:Antibodies, Bacterial / Q000276:immunology; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000302:isolation & purification*; D002352:Carrier Proteins; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D005779:Immunodiffusion; D008297:Male; D009895:Opsonin Proteins / Q000276:immunology; D010587:Phagocytosis; D018805:Sepsis / Q000382:microbiology*; D013290:Streptococcal Infections / Q000209:etiology / Q000382:microbiology; D013291:Streptococcus / Q000032:analysis* / Q000302:isolation & purification / Q000648:ultrastructure; D013297:Streptococcus pyogenes / Q000276:immunology / Q000648:ultrastructure; D019966:Substance-Related Disorders / Q000150:complications
chemical_list: D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D009895:Opsonin Proteins; C014689:streptococcal M protein