Here's some info on useful bacteria for digestion. I hope it helps.
"The bacteria in your GI tract which make up your gut microbiome, play a vital role in your immune system, thyroid function, bone health, and overall health. In fact, scientists discovered that the gut microbiome contains tens of trillions of microorganisms, including up to 1,000 different species of bacteria with over 3 million genes.
"Most of your gut bacteria are meant to be located in your large intestine and colon, where they help break down food, synthesize vitamins, and eliminate waste. When bacteria normally found in the large intestine and colon begin to colonize the small intestine, bacterial overgrowth occurs. Small intestinal bacterial overgrowth can also occur when there is an overgrowth of otherwise normal bacteria in the small intestine itself."
Quoted from "SIBO – Small Intestinal Bacterial Overgrowth: 10 Symptoms & Solutions"