Sugars in human breast milk can kill bacteria directly and break down biofilms that bacteria form as protection.

news.vanderbilt.edu

The sugar is known as human milk oligosaccharides (HMO’s), which have previously been shown to feed beneficial bacteria in the infant’s gut. The HMO’s have now been shown to sensitize target bacteria including Strep B (which many pregnant women test positive for) and then they kill them.