Necrotizing enterocolitis (NEC) is the most common and serious gastrointestinal disorder among preterm neonates. We aimed to assess specific gut microbes associated with NEC. In 2002, an outbreak of NEC occurred in six neonates within a 2-month period in a Canadian neonatal intensive care unit. Recently, C. neonatale and Clostridium butyricum, Clostridium species involved in NEC, were significantly overrepresented among colonic mucosal samples from premature piglets with NEC. The aim of this project is to compare multiple strains of Clostridia that are responsible or not for NEC.