Knoop, Kathryn A.

Abstract Neonatal sepsis remains a leading cause of death in preterm and low-birthweight infants and can be separated into two groups: early-onset sepsis (EOS) and late-onset sepsis (LOS). Previous studies have shown that LOS can result from translocation of enteric bacteria across the intestinal epithelium, resulting in bloodstream infection. Through metagenomic sequencing we have observed, unsurprisingly, potential sepsis-causing organisms such as Escherichia coli, Staphylococcus aureus, Enterobacter cloacae, and Group B Streptococcus (GBS) in the stool of neonatal intensive care unit patients. Our previous work has shown E. coli can disseminate from the intestines via goblet cells in a model of LOS, but how other bacterial pathogens disseminate remains unclear. GBS is often associated with EOS following in utero infections and vertical transmission from the mother during pregnancy and delivery. However, the ability of gut-residing GBS to cause sepsis in a murine model of LOS is still unknown. Here we infected five-day-old mice by oral gavage with different strains of GBS, but we did not observe GBS translocating the intestinal epithelium in the pups, unlike E. coli. We next induced EOS in newborn mice by vaginally inoculating pregnant mice to assess GBS dissemination and compare the EOS model to our LOS model. After in utero infection, most pups were intestinally colonized with GBS and, interestingly, only pups with GBS colonies in the lungs had systemic GBS infections. This data suggests neonates are at risk of GBS infection in utero, but not following delivery, even if GBS colonizes the neonatal intestine. This work could elucidate the pathogenesis of EOS as compared to LOS, leading to a deeper understanding of modes of GBS transmission. Supported by NIH: DK122187

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.

Abstract Sepsis can result from a variety of pathogens, originating from a range of sources. A vast range of presenting symptoms is included in the catch-all term of “bacteremia,” making diagnosis and prognosis particularly troublesome. One underexplored factor contributing to disparate outcomes is the age of the patient. Neonatal sepsis in very-low-birth-weight infants can result in vastly different immunological outcomes unique from sepsis in adults. It is also becoming increasingly clear, both from preclinical experimental models and clinical observations, that the age and history of previous microbial exposures can significantly influence the course of infection from sepsis and cytokine storms to immunopathology. In this study, we will explore key differences between neonatal and adult sepsis, experimental models used to study sepsis, and how responses to the surrounding microbial universe shape development of the immune system and impact, positively or negatively, the course of disease.

AbstractThe increasing incidence of food allergy remains a significant public health concern. Food allergy is partially due to a lack, or loss of tolerance to food allergens. Clinical outcomes surrounding early life practices, such as breastfeeding, antibiotic use and food allergen exposure, indicate the first year of life in children represents a unique time for shaping the immune system to reduce allergic outcomes. Animal models have identified distinctive aspects of when and where dietary antigens are delivered within the intestinal tract to promote oral tolerance prior to weaning. Additionally, animal models have identified contributions from maternal proteins from breast milk and bacterial products from the gut microbiota in regulating dietary antigen exposure and promoting oral tolerance, thus connecting decades of clinical observations on the benefits of breastfeeding, early food allergen introduction and antibiotic avoidance in the first year of life in reducing allergic outcomes. Here, we discuss how exposure to gut luminal antigens, including food allergens, is regulated in early life to generate protective tolerance and the implications of this process for preventing and treating food allergies.

Late-onset sepsis (LOS) and other systemic bloodstream infections are notable causes of neonatal mortality, particularly in prematurely born very low birth weight infants. Breastfeeding in early life has numerous health benefits, impacting the health of the newborn in both the short-term and in the long-term. Though the known benefits of an exclusive mother’s own milk diet in early life have been well recognized and described, it is less understood how breastfed infants enjoy a potential reduction in risk of LOS and other systemic infections. Here we review how gut residing pathogens within the intestinal microbiota of infants can cause a subset of sepsis cases and the components of breastmilk that may prevent the dissemination of pathogens from the intestine.

Late-onset sepsis (LOS) is a highly consequential complication of preterm birth and is defined by a positive blood culture obtained after 72 h of age. The causative bacteria can be found in patients’ intestinal tracts days before dissemination, and cohort studies suggest reduced LOS risk in breastfed preterm infants through unknown mechanisms. Reduced concentrations of epidermal growth factor (EGF) of maternal origin within the intestinal tract of mice correlated to the translocation of a gut-resident human pathogen Escherichia coli , which spreads systemically and caused a rapid, fatal disease in pups. Translocation of Escherichia coli was associated with the formation of colonic goblet cell-associated antigen passages (GAPs), which translocate enteric bacteria across the intestinal epithelium. Thus, maternally derived EGF, and potentially other EGFR ligands, prevents dissemination of a gut-resident pathogen by inhibiting goblet cell-mediated bacterial translocation. Through manipulation of maternally derived EGF and alteration of the earliest gut defenses, we have developed an animal model of pathogen dissemination which recapitulates gut-origin neonatal LOS.