Final answer:
Lactobacillus is a bacteria that competes with C. diff in the gut by creating an unfavorable environment and producing antimicrobial substances.
Step-by-step explanation:
The bacteria that competes with C. diff is Lactobacillus. While both C. diff and Lactobacillus are present in the gut, Lactobacillus helps maintain a healthy balance by producing lactic acid, which creates an unfavorable environment for C. diff to thrive. Additionally, Lactobacillus produces antimicrobial substances that can inhibit the growth of C. diff.