Oh, it's a strain of lactobacillus paracasei that has a track record of being beneficial for gut ecology, like the many other strains of probiotics out there. Pure strain in Yakult, nothing else. Don't think this strain was ever tested as an adjunct in cheese for either coliform control (it does produce bacteriocins) or for flavor enhancement. Decent studies were done showing health benefits.
If you reculture at home, use skim milk in a typical yogurt process, except keep the temp at 99F, as that is the optimal growth temperature for this strain. Ability to keep successive generations going depends on your handling technique and cleanliness. If you make yogurt, you can also add this strain in and keep it as part of the overall blend.