Necrotizing enterocolitis (NEC) is a leading cause of morbidity and mortality among infants in the neonatal intensive care unit (NICU). Prematurity is the most important risk factor for NEC. The pathogenesis of NEC remains unclear, and prevention and treatment strategies are limited. It has been postulated that abnormal colonization of the preterm gut, or an unfavorable balance between gut bacteria, is significant in the pathogenesis of NEC.