My apologies for any confusion. The recommendation is that there be two different types of bacteria, and there's no specification that it MUST be any particular ones, just that they be different (some yogurts only contain acidophilus)

Acidophilus, bifidus and bulgaricus are different strains of lactobacillus. Thermophilus is a beneficial strain of streptococcus.

I'll go back and edit my other post, just to avoid confusion for other readers!

Happy yogurt making!

Doreen