Final answer:
Fecal transplants introduce healthy bacteria into the patient's gut and help stimulate the production of immune cells that can kill invading bacteria.
Step-by-step explanation:
When a patient undergoes a fecal transplant, the healthy bacteria from the stool sample colonize in the patient's gut. These bacteria then interact with the patient's immune system, stimulating the production of immune cells that are capable of killing invading bacteria.
Essentially, the healthy bacteria from the transplant help strengthen the patient's immune response and provide protection against future infections. For example, the bacteria that overgrow when normal gut bacteria are lost due to antibiotic use, such as Clostridium difficile, can be effectively treated with fecal transplants.