Duodenal microflora in very-low-birth-weight neonates and relation to necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergen cy in the neonatal period. Small-bowel overgrowth with aerobic gram-negativ e bacteria has previously been implicated in the development of NEC. This p rospective study performed quantitative bacteriology on 422 duodenal aspira tes collected from 122 very-low-birth-weight (<1,500-g) newborns, at the ti me of routine changing of nasogastric tubes. Isolates of Enterobacteriaceae were typed by repetitive extragenic, palindromic PCR and pulsed-field gel electrophoresis. One or more samples from 50% of these infants yielded gram -negative bacteria, predominantly Escherichia coli, Klebsiella spp., and En terobacter spp. with counts up to 10(8) CFU/g. The proportion of samples wi th gram-negative bacteria increased with postnatal age, while the percentag e of sterile samples declined. Molecular typing revealed marked temporal cl ustering of indistinguishable strains. All infants had been fed prior to is olation of gram-negative organisms. Antibiotic use had no obvious effect on colonization with Enterobacteriaceae, There were 15 episodes of suspected NEC (stage I) and 8 confirmed cases of NEC (2 stage II and 6 stage III) dur ing the study period. Duodenal aspirates were collected prior to clinical o nset in 13 episodes of NEC. Seven of these yielded Enterobacteriaceae, of w hich five strains were also isolated from infants without NEC. Very-low-bir th-weight infants have high levels of duodenal colonization with Enterobact eriaceae, with evidence of considerable cross-colonization with indistingui shable strains. There was no association between duodenal colonization with particular strains of Enterobacteriaceae and development of NEC.