At two in the morning, a reel says a sick baby's spit tells her mother's milk what to fight, and twelve mothers have it before sunrise. Part three of three: in a 2025 study of 195 mothers and babies, which bacteria in breast milk settle in a baby's gut, and which travel the other way.
After one dose of an antibiotic, fewer than three Salmonella could infect a mouse; without the dose, it took about 100,000. Part two of three, on how the microbiome works and why a body needs it: bacteria in the gut and on the skin keep germs out, and a 2024 review of the microbiome argues that they help set the body's targets every day.
Breast milk delivers millions of bacteria a day to a baby, and in 1899 a doctor in Paris saw that it also picks which ones win the gut. Part one of three: milk carries sugars only those bacteria can eat, a recount of a 2009 chart shows what a well-known map of the microbiome measured, a four-day course of antibiotics can leave some of them missing for months, and a 2024 review of the microbiome asks what a body is once its microbes count.