E. X. Zhang1, P. T. Delaplain2, J. Wang2, A. V. Grishin2, H. R. Ford3 1Shady Side Academy,Pittsburgh, PA, USA 2Children’s Hospital Los Angeles,Pediatric Surgery,Los Angeles, CA, USA 3University of Miami,Leonard Miller School Of Medicine,Miami, FL, USA
Introduction: Necrotizing enterocolitis (NEC), a severe inflammation of the small intestine in premature neonates, is associated with bacterial colonization of the gut. We believe that the first colonizers of the gut may be either opportunistic pathogens or innocuous/protective bacteria. Artificial introduction of protective bacteria may be an efficient method of protecting against NEC. Enterococcus faecalis is one of the most common first colonizers of the intestine. There are multiple strains of E. faecalis, some of which could be protective. In this study, we investigated the efficiency of colonization of the intestines of neonatal rats with different strains of E. faecalis.
Methods: 20 strains of E. faecalis possessing different combinations of biochemical phenotypes (hemolysis, sorbitol fermentation, kanamycin resistance, gelatin liquefaction, beta-galactosidase, xifaxan resistance) were previously isolated from 4-day old rats. Liquid cultures of these strains, grown in BHI medium, were mixed in equal proportions, and 10^8 cfu total were introduced to newborn rats with formula during their first feeding. After four days of the formula feeding – hypoxia, NEC-inducing regimen, samples of intestinal content from different animals were plated on blood agar-azide to isolate E. faecalis. Strains were identified by replica plating of E. faecalis colonies onto appropriate diagnostic media.
Results: Intestinal loads of E. faecalis on day 4 varied from 10^4 to 10^7 cfu/mL. In all animals examined, E. faecalis populations were dominated by strains different from those that were artificially introduced, presumably acquired from their mothers. Of the introduced strains, only BB70 and 269 were found in large numbers.
Conclusions:
1. Four days after the artificial introduction of E. faecalis, loads of these bacteria differed by three orders of magnitude.
2. Maternally-derived strains of E. faecalis dominated the populations.
3. BB70 and 269 were the most consistent colonizers of the neonatal intestine.
Identifying efficient first colonizers among common intestinal bacteria is an important step towards creation of artificial bacterial communities with protective properties against NEC.
