Growth characteristics of group A streptococci in a new chemically defined medium.

A new chemically defined medium for the growth of group A streptococci has been formulated. The advantages of this new medium over previously described defined media are: (i) rates of growth (i.e., doubling times) of 20 strains were comparable to the rates of growth in complex media; (ii) each strain grew to a higher culture density in the new defined medium than in complex media; (iii) transfer from complex media with small inocula was possible without any prior adaptation regimen; and (iv) the production of virulence factors (i.e., M protein and hyaluronic acid) and extracellular enzymes during growth in this new medium was comparable to that in complex media.