Timeline of sample collection from NEC and control patients. Included subjects were born between 24–32 weeks gestation and stool samples were collected weekly from birth to 10 weeks of life. Panel A - 16S rRNA-based microbial community analyses were performed on samples from throughout this period and indicated a shift in microbial communities at approximately 2 weeks after birth. Panel B - Shotgun DNA sequencing of metagenomes from samples on the day of NEC diagnosis and one week before showed no significant difference. Panel C - Subsequent shotgun sequencing of metagenomes focused on the interim period.