P. T. Delaplain1, J. Wang1, A. Grishin1, H. R. Ford1,2 1Children’s Hospital Los Angeles,Pediatric Surgery,Los Angeles, CA, USA 2University Of Miami,Miller School Of Medicine,Miami, FL, USA
Introduction: The exact relationship between intestinal bacterial populations and the development of necrotizing enterocolitis (NEC) is currently unknown. We hypothesize that strains of bacteria colonizing the neonatal gut could be either innocuous/protective, or opportunistically pathogenic. We investigated the ability of two different strains of E. faecalis, one of the common first intestinal colonizers, to induce or prevent intestinal inflammation in neonatal rats.
Methods: Strains of E. faecalis previously isolated from 4-day-old rats were examined for a variety of characteristics and two strains, 8 and BB70, were chosen for in vivo experiments. Newborn rats from timed pregnant mothers were formula-fed and subjected to hypoxia every 8 hours to induce NEC. Neonates were inoculated with or without 108 cfu of E. faecalis 8 or BB70 during the first feed. During the second feed, the animals were challenged with, or without 106 cfu of Cronobacter muytjensii 51329, a known NEC pathogen. All animals were sacrificed on day 4. Intestinal contents were serially diluted and plated on blood agar, BHI-azide agar, and MRS agar to quantify total bacteria, E. faecalis, and lactic bacteria. Isolates from BHI-azide were further examined using diagnostic media to identify E. faecalis strains. NEC was scored histologically. Results were compared using χ2 test.
Results: Strain 8 and Strain BB70 were found in the intestines of animals inoculated with these strains at average relative abundance of 28.2% and 49.5%, respectively. These strains were not found in control animals. Strain 8 increased NEC pathology, whereas strain BB70 decreased it (Figure 1).
Conclusion: E. faecalis strains 8 and BB70 appear to act as opportunistic pathogen and protective commensal, respectively. Our results show that pathogenic and protective properties of E. faecalis may be strain-specific. E. faecalis strains similar to BB70 may be useful in preventing clinical NEC.
