Fecal collection
All fecal samples were collected within 48 hours using Zymo DNA/RNA
ShieldTM fecal collection tubes (Zymo Research, U.S.).
At least 1 g or 1 ml of neonates’ feces were collected, mixed, and then
stored at 2-25°C before being transferred into a
-80°C freezer for storageg. The date and time of fecal
sample collection were recorded to determine the neonatal age at the
time of sample collection.