At a Glance

Every meal feeds the body and its microbes.

1. Part 1Milk sugars feed only some bacteria: every feed has two eaters.
2. Part 2When fiber runs short, gut bacteria turn to the mucus coat.
3. Part 3One gut makes butyrate or TMAO, depending on the meal.
4. Part 4Milk carries food and seed together; the gut decides if the seed takes.

What a germ does depends on who already lives there.

1. Part 1A probiotic label counts what goes in, not who stays.
2. Part 2The same germ meets a different crowd in each body.
3. Part 3Healthy mice took 100,000 Salmonella; after one antibiotic dose, fewer than three.
4. Part 4In a baby's gut, one kind of Bifidobacterium usually took over.

Antibiotics hit the whole crowd, not just the germ.

1. Part 1Four days of pills; six weeks to come back; nine species still gone at six months.
2. Part 2Kill the butyrate makers and oxygen gets in; Salmonella and C. difficile follow.
3. Part 3Protection from microbes can be lost to one dose of the wrong drug.
4. Part 4Babies carried tetracycline-resistance genes, and so did the milk.

Body and microbes each act on the other.

1. Part 1Lose the gut microbes and the brain's seal changes.
2. Part 2Bacteria feed the gut cells; the cells keep the oxygen low for them.
3. Part 3Microbes may be a second hand choosing the body's targets.
4. Part 4Mouth strains in milk: milk may be half of a loop.

Keep what was measured apart from what was guessed.

1. Part 1The microbiome pie shows what one project chose to study.
2. Part 2Samples show who shares strains, not who passed them to whom.
3. Part 3Gut bacteria predicted fever, and a link does not prove a cause.
4. Part 4Two ways of reading DNA find two different crowds in milk.