General Information: Lactobacillus casei str. Zhang was isolated from traditional home-made koumiss (fermented mare's milk) in Inner Mongolia, China. This strain has the potential probiotic properties such as high resistance to acidic pH and bile salt. They are commonly found in the oral, vaginal, and intestinal regions of many animals. They are important industrial microbes that contribute to the production of cheese, yogurt, fermented milks, and other products, all stemming from the production of lactic acid, which inhibits the growth of other organisms as well as lowering the pH of the food product. Industrial production requires the use of starter cultures, which are carefully created, cultivated, and maintained, which produce specific end products during fermentation that impart flavor to the final product, as well as contributing important metabolic reactions, such as the breakdown of milk proteins during cheese production. The end product of fermentation, lactic acid, is also being used as a starter molecule for complex organic molecule syntheses. Lactobacillus casei is used as a starter culture during milk fermentation and for the flavor development of certain bacterial-ripened cheeses.