Probiotics: Viable single or mixed culture of microorganisms which when applied to animal or human, beneficially affects their host by improving the properties of the indigenous microflora. 
Over the last decade, other definitions have been applied to the term, but they all basically agree, at least in general terms. The increased interest in defining exactly what probiotics are has arisen, in large part, from the increasing demand for them. Probiotics have found application in a wide variety of products including, yogurt, dietary supplement capsules, tablets, milk, butter, cheese, salami, soy sauce, sour dough.  They-are even being used as antimicrobials for the poultry industry due to their ability to inhibit salmonella growth in chickens.
Probiotics are clearly here to stay and the market, despite its incredible growth over the last few years, is still in its infancy. Presently, there are identifiable trends in the use of probiotics. These trends can be generalized as a heightened awareness of differing quality in the organisms. From the manufacturing side, that includes such things as production of-well-documented, clinically-backed strains, ability to survive gastric acid and bile salts, adherence, long-term stability. Also issues such as milk/casein-free are important for consumers. [3,4]
From the end-user or medical perspective all the above are important, but there are additional considerations. The additional considerations all boil down to; what is the best way to use the probiotics in the most clinically efficacious manner?
Ten years ago, most probiotic products contained either Lactobacillus acidophilus or Bifidobacterium lactis (bifidum). If one was really lucky, they could find a combination of the two and possibly a couple of yogurt strains (i.e., Lactobacillus bulgariucus) thrown in. Many of these contain only a few hundred million viable cells at the time of manufacture. While that may sound like a lot of organisms, especially when we are conditioned to think of bacteria as being "bad," current data tells us that those numbers were probably far too low to be doing very much good. At least in the short-term, therapeutic application of the probiotics.
As more and more data comes in, it is becoming apparent that at least a billion organisms are needed per dose to achieve any real clinical significance. In a recent study, ten billion Bifidobacterium in milk per day were given and immune markers measured.  A significant increase...