According to the Dairy Connection, the Mesophilic M culture contains 3 separate cultures:
Lactococcus lactis subsp. lactis
Lactococcus lactis subsp. cremoris
Lactococcus lactis subsp. lactis biovar diacetylactis
For soft ripened, and fresh (unripened) cheeses:
Brie, Camembert, Havarti, Gouda, Edam, Feta, Blue, Chevre, etc…
Mesophilic A only contains 2:
Lactococcus lactis subsp. lactis
Lactococcus lactis subsp. cremoris
For semi-soft and fresh cheeses:
Cheddar, Colby, Monterey Jack, Feta, Chevre, etc…
I assume it’s the extra culture in “M” that’s needed for the other cheeses.
I made a gouda with the “A” culture from New England Cheesemaking. They don’t call it “A” and they don’t seem to have the “M” culture but they say there’s can be used for Cheddar, Monteray Jack, Stilton, Edam, Gouda, Muenster, Blue, and Colby.
Sal