Here’s another reason to consider breast-feeding: Some mothers’ milk may protect newborn babies from a serious bacterial infection.

A study by researchers at Imperial College in London involving nearly 200 African women found that a sugar found in breast milk may ward off Group B streptococcus [streptəˈkɑkəs]. About one in three women carry the bacteria, which can be transferred to an infant during birth and cause a life-threatening infection.

The researchers tested the women for a particular genetic system that determines the sugar composition of breast milk. Each woman’s breast milk is a mixture of sugars, which help feed beneficial bacteria in a baby’s intestine. They also tested the mothers and babies for the streptococcus bacteria at intervals up to 90 days after birth.

Women who had a specific genetic system known as Lewis genes were less likely to carry the streptococcus bacteria, researchers found. Also, the babies whose mothers produced the protective sugar were more likely to have cleared the bacteria from their bodies after 60 days than those whose mothers didn’t produce it. The findings were published in the journal Clinical & Translational Science.

Researchers believe the sugar allows beneficial bacteria to flourish in a baby’s gut, effectively crowding out harmful bacteria. The protective sugar also may act as a decoy that attracts harmful bacteria and flushes it from the body.

While only about half of women produce the sugar that fights streptococcus, researchers said the findings could lead to new treatments, such as breast milk sugar supplements.

Breast-feeding can be a challenge for some, but it is one of the most effective ways for new moms to protect their baby’s health.