Probiotics kill harmful bacteria in the intestine, such as Clostridium. Lactobacillus acidophilus, Lactobacillus casei, Bifidobacterium bifidium, and other active microorganisms are found in probiotic milk products. These bacteria keep the balance of gut microbes in check by increasing the population of beneficial germs like Clostridium and decreasing the population of harmful microbes like Clostridium.