Streptococcus pyogenes (group A Streptococcus; GAS) requires flexible metabolic regulation to adapt to diverse host environments; however, its physiological responses to lactose and glycerol remain poorly characterized compared with glucose. In this study, we analyzed three representative serotype M1 GAS strains--the M1global strain 5448, the ancestral M1 strain SF370, and SP1380 as a representative of the recently emerged M1UK lineage. Glycerol consistently suppressed lactose-dependent growth a