The microbial ecology of necrotising enterocolitis
Abnormal gastrointestinal colonisation has been implicated in the development of necrotising enterocolitis (NEC). Organisms capable of rapid fermentation of excess carbohydrate in the small bowel were postulated to produce adverse intraluminal conditions leading to intestinal injury. Quantitative culture of duodenal aspirates from 122 very low birth weight newborns revealed a high prevalence of Gram-negative colonisation, with counts up to 108 cfu/g. Gram-negative colonisation occurred in infants who had been fed, increased with postnatal age and was associated with a longer stay on the neonatal unit. Molecular typing of E. coli, Klebsiella spp. and Enterobacter spp. demonstrated marked temporal clustering of indistinguishable strains. Colonisation with particular strains of Enterobacteriaceae was not associated with subsequent development of NEC. Faecal flora, from NEC cases and control infants, comprised predominantly aerobic Gram-negative organisms and enterococci, with anaerobes isolated infrequently. Prior to clinical onset of confirmed NEC, Enterobacteriaceae isolates remained at high levels or increased, while there was a significant fall in enterococci. This fall in enterococci was not apparent in infants with suspected NEC. Asymptomatic infants were colonised with Enterobacteriaceae isolates indistinguishable from NEC cases, but enterococci were also present in high numbers, often being the predominant strain. One E. coli from a post-mortem peritoneal sample, was fully induced for b-galactosidase expression. Isolates identical by PFGE, from the same infant and controls were not induced. Other strains, from NEC cases and control infants, showed no difference in b-galactosidase activity. NEC appears not to be associated with colonisation with particular strains of Enterobacteriaceae, but the decline in enterococci preceding NEC should be investigated.