Influence of growth conditions on expression of immunoglobulin G binding in group A streptococci

Many group A streptococci (GAS) bind the Fc part of IgG. In the present wor k, the possible influence of growth time and incubation atmosphere on the e xpression of the IgG binding activity by GAS of various serotypes was studi ed. Among 13 GAS reference strains, two categories were distinguished on ae robic incubation at 37 degrees C, one expressing similar IgG binding activi ty at 6 h and 18 h (types M1, M4, M13, M15), and a second one which showed higher binding at 6 h than at 18 h (M9, M14, M22, M25, M48, M49). Only one strain (M36) bound less IgG at 6 h than at 18 h. Seven of the strains (M5, M6, M22, M25, M36, M48, M49) showed higher binding of IgG when grown in a 5 % CO2 atmosphere than in air, whereas one strain (M14) showed a reverse pat tern and in the remaining five strains, no influence was found. Protease ac tivity was detected in the growth supernatant of most of the strains. For f ive selected strains, the time of appearance of supernatant protease activi ty coincided with a decay of surface IgG binding activity. Purified strepto coccal cysteine protease was found to reduce or abolish the binding of IgG by each of three studied strains (M1, M13 and M15) and of type M1 or M15 pu rified IgG binding material. When tested in the stationary phase, a majorit y of 62 clinical GAS isolates belonging to 6 different M types showed high protease activity but low binding of IgG. We conclude that streptococcal Ig G binding is often better expressed on growth in 5% CO2 atmosphere than in air. Furthermore, due to its sensitivity to streptococcal protease, the IgG binding activity is mostly higher during the logarithmic than during the s tationary phase of growth.