P03 – The Impact of Antibiotics on Neonatal Rat Microbiota and the Development of Experimental Necrotizing Enterocolitis

Author(s):
Joanna Lim, Brandon Bell, Debi Thomas, Stephanie Papillon, Jin Wang, Larry Wang, Anatoly Grishin, Henri Ford, CHLA

Background: Necrotizing enterocolitis (NEC) is the most lethal disorder affecting premature infants but the etiology is not understood. Cronobacter sakazakii is one of a few opportunistic pathogens that have been implicated in clinical and experimental NEC. In our previous studies, C. sakazakii dramatically increased the incidence and severity of NEC in neonatal rats. We sought to examine the effect of antibiotic therapy on the neonatal microbiome and putative opportunistic pathogens that have been implicated in the pathogenesis of NEC.

Hypothesis: Antibiotic prophylaxis against opportunistic pathogens will decrease the incidence and severity of NEC.

Methods: Newborn rats were fed conventional formula and subjected to hypoxia (5% O2 for 10 minutes) thrice daily. One group received untreated formula and the other received formula inoculated with C. sakazakii (10^7 CFU/100 µl). Each was further randomized to receive ampicillin (25-30 mg/kg) or an equivalent volume of untreated formula starting on day of life #1. The rats were sacrificed on day of life #4. The terminal ileum was examined histologically and by culture-based characterization of the microbiota, by sequencing a variable region of 16S rRNA. The maternal and neonatal stool microbiota were similarly examined.

Results: Addition of C. sakazakii to the formula resulted in an overall paucity of organisms and increased incidence of NEC compared to rats that received untreated formula. Administration of ampicillin prevented the development of NEC. Stool cultures showed progressively greater counts of C. sakazakii with each day.

Conclusions: Antibiotic prophylaxis prevented the development of NEC in a model that otherwise produced a 50% incidence of NEC. The paucity of bacteria may reflect that inoculation of C. sakazakii affected the microbiome but failed to colonize. Further studies should be done with antibiotic resistant strains to separate the effect of the antibiotic on the microbiome from that on specific opportunistic pathogens.