Although the pathogenesis of necrotizing enterocolitis (NEC) has yet to be delineated, there is ample evidence to support a role of intestinal bacteria in the genesis and complications of this disease in neonates. The importance of coliform bacilli has been demonstrated in experimental NEC in newborn rats, and sporadic outbreaks of NEC in neonatal intensive care units have frequently been associated with intestinal colonization or septicemia caused by various members of the Enterobacteriaceae family.1,2 Stanley and Null3 reported that temporal alterations in the intestinal microflora of infants were correlated with changes in the incidence of NEC and that neonates initially colonized with Klebsiella pneumoniae had an almost threefold greater likelihood of developing disease than those colonized with other enterobacterial species. Surveillance studies from one intensive care unit have shown that K pneumoniae and Escherichia coli strains are recovered significantly (P <.01) more often from rectal cultures of infants