The only helpful bacterium found in humans is found in the stomach?

hmmm

Explanation:

I'm pretty sure it's either bifidobacteria or lactobacillus

Possibly Probiotics

they are very helpful to the  human gut

Or the most 2 helpful bacteria are Lactobacillus and Bifidobacteria

Explanation:

< > according to newton's third law of motion, forces always act in equal but opposite pairs. another way of saying this is for every action, there is an equal but opposite reaction.< >