I read a report written by a bacteriologist, it was a book really, published in the 1950's(lapis posted the link),the author observed bacterial microbes "morphing" into other species under a microscope, therefore I do not advocate friendly bacteria simply because friendly bacteria in the wrong environment aka body fluids, can morph into biotoxic, non friendly bacteria.
Also millions are lactose and dairy intolerant and do not know it. I do not drink milk or eat dairy because I do not want the accumulations and bacteria, friendly or not.
I drink almond milk, made from almonds and canned coconut milk and use plant oils instead of dairy, milk, butter or cheeze.