Is there a DIY way? Is it possible to make a bacteria strain from scratch based on an existing one ? (for example lactobacillus reuteri).
I did a master's thesis involving enzymes from a probiotic bacteria. Many of the known probiotics were cultivated from faeces but others have also been isolated from breastmilk. Many of the probiotic bacteria are strict anaerobes and can only be succesfully cultivated in modified atmosphere. You may need to use selective plating with various prebiotic compounds such as Galactooligosaccharides or similar compounds in order to control bacterial growth. I recommend incubating at 37°C or slightly below depending on how well controlled your incubator is.