All of the TRUE about M proteins of Streptococci, EXCEPT:
Correct Answer: M2 serotypes are most commonly associated with invasive diseases and Toxic Streptococcal Syndrome
Description: M proteins have been divided into two groups: Those in group I have a paicular set of repeating sequences and are associated with Streptococci that cause acute Rheumatic fever (rheumatogenic strains). Those in group II produce Opacity factor, do not have the same set of repeating sequences and do not cause rheumatic fever. The synthesis of M proteins is controlled by the so called virulence regulon that encodes M protein, Streptococcal C5a peptidase and opacity factor. The emm gene of S. pyogenes is the gene that encodes the M protein. The M protein, responsible for the bacterium's capacity to resist phagocytosis, is a major virulence factor in GAS. The 5' ends of emm genes are highly heterogeneous and encode for the serotype specificity used for the M-typing system Community-based outbreaks of paicular streptococcal diseases tend to be associated with ceain M types; therefore, M serotyping has been very valuable for epidemiologic studies. M1 serotypes are most commonly associated with invasive diseases and Toxic Streptococcal Syndrome. Acquired immunity to streptococcal infection is based on the development of opsonic antibodies directed against the antiphagocytic epitopes of M protein. Although such antibodies protect from infection against a homologous M protein type, they unfounately confer no immunity against other M types. This observation is one of the factors that represent a major theoretical obstacle to the S pyogenes vaccine design because more than 80 M serotypes have been described to date. Ref: Color Atlas and Diagnostic Microbiology by Elmer.W.Koneman; 5th edition
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