All bacteria in the gut comes from the environment and is ingested during feeding. While the mother's milk should be sterile, other environmental factors allow bacteria to enter. Bacteria colonises the mouth first. It is swallowed in large numbers along with the milk. For the first couple of days after the birth, baby will pass meconium. This is a sticky, greeny-black substance that has built up in baby's intestines during pregnancy and is made up of bile, mucus, cells from the bowel wall, secretions and amniotic fluid. While meconium may be difficult to wipe off that tiny bottom, its appearance is a good sign that baby's bowels are working normally. After a day or two, once feeding is established and the last of the meconium passes out, the stools will turn a browny-green and be loose and grainy in texture, before becoming more yellow