Since I have seen many religious people drink fresh spring water, I assume that there is no concern regarding the kashrut of microorganisms in the water such as hydra and paramecia, among other similar creatures.
Similarly, certain products such as probiotics, commonly present in yogurt, contain bacteria. Some oral vaccines (It's been a while since I got the Sabin vaccine - I assume they still use it) contain viri. I assume that here, too, there is no concern regarding kashrut.
Why was there no concern considering that these are living "species"? Are they in its own non-animal category? Does the Talmud or other source discuss these? If so, where?