Assistant Professor Annie Hoen discussed her most recent research as part of the Geisel School of Medicine’s Microbiology/Immunology Seminar. (Credit: Sam Reed ’19)

Annie Hoen, Assistant Professor of Epidemiology and Biomedical Data Science at the Geisel School of Medicine, has been a member of the Dartmouth family for nearly a year to date. Her work concerns the microbiome of the infant gut, the factors that contribute to its formation, and its effects on health during infancy.

The microbiome is the population of microbes living in and on the body that is acquired from an individual’s environment. This population of microbes is hugely relevant to human health, providing both innate and adaptive immunity to pathogens. The microbiome has been linked to allergy development, the vaccine and drug efficacy, and numerous other factors.  For the purposes of Hoen’s work, only the bacteria of the microbiome are examined.

Hoen uses the New Hampshire Birth Cohort as a source of data. The cohort involves approximately 1,500 mothers whose children have stool samples taken periodically. Hoen tests these samples using a 16S rDNA test, which can detect the ribosomal DNA (rDNA) of different bacteria, which codes for ribosomal RNA (rRNA), to determine the diversity of the infant’s gut microbiome. Hoen’s data show that the two foremost determinants of an infant’s gut microbiome are delivery method, vaginal or c-section, and feeding method, breast milk or formula. Differences in either method result in vastly different microbiomes.

In the case of delivery method, the area of the mother’s body the baby is first in contact with characterizes its first significant microbial exposure, affecting its microbiome for much of its early life. Hoen’s most recent study, published February 1st, 2016, showed that a baby delivered by c-section and wiped with a pad of gauze which was first rested in the vagina would develop a gut microbiome more similar to that of a baby delivered via vaginal birth, indicating that the vaginal environment provides a unique microbiome.

In many ways, natural methods of feeding and delivery are beneficial to infant health. To provide evidence for this claim, as well as to gain insight into important aspects of the infant gut microbiome, Hoen studied a cohort of 22 infants with cystic fibrosis at Dartmouth Hitchcock Medical Center. 16S rDNA tests were done on airway and stool samples, and colonization times of Pseudomonas, a bacteria marking the onset of cystic fibrosis, were also measured. The findings revealed that breastfeeding resulted in a later colonization of Pseudomonas, or a longer period of health, as did a more diverse gut microbiome, which is contributed to by vaginal delivery. This is just one of many studies with which Hoen has been involved that shows how feeding and delivery methods impact health.

Going forward, Hoen hopes to study more environmental factors, in addition to delivery and feeding, that affect the microbiome. This analysis would provide more knowledge in determining factors that affect infant health.