What organisms grow in yogurt?

The term "live and active cultures" on a yogurt label refers to Lactobacillus bulgaricus and Streptococcus thermaophilus, living organisms used to ferment pasteurized milk into yogurt (some yogurts also contain Lactobacillus acidophilus, Bifidus and other cultures). These tiny critters break down milk lactose, giving the lactose-intolerant among us a better chance of getting the nutritional benefits of a milk product without suffering the side effects.