Characteristics of The Extracellular M Proteins of Group-A Streptococci

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Abstract
M protein was detected in the concentrated broth-culture supernates of strains of group-A streptococci, belonging to a wide variety of M types, by double-diffusion in gel, and its presence was confirmed in several strains of M-type 12 by complement fixation with absorbed anti-M serum and by the neutralization of human bactericidal antibody. Extracellular M proteins retained their serological activity after heating at 95.degree. C for 10 min at neutral or acid pH, but were destroyed by proteolytic enzymes. Both the acid-extracted and extracellular M proteins of a type-12 strain had isoelectric points between pH 5.0 and 5.1. The ratios of extracellular to acid-extractable M protein were significantly higher in M types associated with pyoderma than in those associated with infection of the upper respiratory tract. This was related to a striking tendency for skin strains to have less extractable M protein than many of the throat strains, and to the fact only 50% of the throat strains had detectable extracellular M protein. The majority of skin strains (18 of 21) produced extracellular M antigen. The MW distribution in extracellular and acid-extracted M proteins was inferred from chromatography on Sephadex G100 of culture supernates and corresponding acid extracts. In the respiratory M-types 5, 12 and 30 the range of MW was wide (5000 to .gtoreq. 150,000) and very similar in the 2 preparations. In the skin serotypes 49, 55, 57 and 60 extracellular M protein fell into the range 55,000 to .gtoreq. 150,000, a distribution strikingly different from that in the acid extracts of the corresponding strains (5000 .gtoreq. 150,000). Acid extraction may modify the M proteins of pyoderma serotypes more than those of respiratory serotypes.