Floyd, Alex

Abstract The microbiota present on every mucosal surface of the body is imperative for the development and maintenance of the immune system. Disruption of the microbiota from environmental factors can affect immune components in both the mucosal and the systemic immune compartments. Following birth in mammals including humans and mice, the microbiota rapidly develops and matures into a composition generally seen in adults when infants are weaned. Gut microbiota composition is directly affected by feeding type, breast-fed vs formula-feeding, in humans, and the microbiota associated with breastfeeding has been shown to promote intestinal health. As the composition of breastmilk changes throughout lactation, we hypothesize maternal provided factors within breastmilk support the development of the microbiota in a temporally sensitive manner. To address this question we asynchronously cross-fostered (ACF) litters born on day 1 to dams who had delivered 2 weeks earlier. Gut microbiota composition was assessed by 16S analysis of stool samples at the time of weaning, and while the microbiota of synchronous cross-fostered pups resembled the microbiota of their foster dam, the microbiota of ASF mice was different from both their foster dam and the healthy microbiota seen in weanling mice. ACF mice had a significant reduction in bacteroides and firmicute species, species that generally represent the majority of the bacteria within a healthy microbiota, and expansion in prevotella species, which include clinically important opportunistic pathogens, suggesting ACF mice contain a dysbiotic microbiota. Future work will explore and identify what temporally dependent components in breast milk support the development of a healthy microbiota.

Abstract Late-onset neonatal sepsis (LOS), a significant cause of morbidity and mortality in prematurely born infants, results from a bloodstream infection of gut-originating bacteria. It remains unclear how such bacteria translocate from the intestine, though it has been repeatedly observed that breastfed infants, particularly those fed mother’s own milk (MOM), have reduced risk of LOS compared to formula fed infants. Epidermal growth factor (EGF) promotes intestinal barrier function in infants and is present at high concentrations in breast milk post-partum and decreases throughout lactation. We found reduced concentrations of EGF in the stool of premature formula-fed infants compared to MOM-fed infants, and observed a similar decrease in EGF concentrations of stool of neonatal mice asynchronously cross-fostered (ACF) to dams that had delivered two weeks prior. LOS bloodstream isolates of E. coli colonized the tracts of all pups but translocated and disseminated systemically only in ACF mice resulting in bacteremia and rapid death. Goblet cell intrinsic sensing of EGF via the epidermal growth factor receptor (EGFR) limited bacterial translocation from the colon. Oral gavage of recombinant EGF reduced bacteria translocation and prevented the development of systemic disease in ACF mice. Thus, disruption of maternally delivered EGF in ACF mice results in translocation of pathogens from the gut, and a sepsis-like disease. In conclusion we have identified a mechanism whereby a gut-residing pathogen gains systemic access and have developed a novel animal model replicating this mechanism to explore the protective effect of breastmilk and EGF in LOS.