(PTFS02-02-25) Associations Between Extent of Human Milk Exposure and Antimicrobial Resistance in Infant Stool Microbiotas

Objectives: To measure the impact of extent of human milk exposure on antimicrobial resistance (AMR) at different ages.

Methods: This longitudinal cohort study analyzed antimicrobial resistance in infants at ages 1, 3, 6 months, cross-sectionally. Stool samples (n=99) were collected: 1 month (n = 16), 3 months (n = 36), 6 months (n = 47). Study participants for this analysis were recruited from the Michigan Archive for Research on Child Health (MARCH), the Archive for Research in Child Health (ARCH) and BABY GUT (BG). Fecal samples were collected by the infant’s caregiver and returned to the lab by US mail. Genomic DNA was extracted from stool samples, and Takara SmartChip 160 Real-time quantitative PCR was performed to quantify AMR genes.

Results: In 1-month-old and 3-month-old infants, those exclusively formula-fed have higher richness in antimicrobial resistance genes (ARGs) compared to those exclusively breastfed. However, the Shannon diversity index and inverse Simpson index for ARGs are similar. Further, the alpha diversity of mobile genetic elements (MGEs) between formula-fed and breastfed infants are similar. In six-month-old infants, exclusive formula feeding positively associated with Shannon and inverse Simpson alpha diversity indices for MGEs, compared to exclusive breastfeeding. However, the richness of MGEs is similar between the two groups. The alpha diversity of ARGs is similar in formula-fed and breastfed 6-mos-old infants. At each time point, three or fewer infants were exposed to antibiotics in the 30 days prior to stool sampling. For one-month-old infants, three with antibiotic exposure had increased alpha-diversity (Shannon and inverse Simpson) in their ARGs.

Conclusions: Differences in alpha diversity of ARGs and MGEs were observed, with formula-fed infants showing higher diversity and richness compared to breastfed infants at certain time points.

Funding Sources: This research was funded in part by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), the Office of the Director at the National Institutes of Health, the Michigan Health Endowment Fund and by the Center for Research in Autism, Intellectual and Neurodevelopmental Disabilities (C-RAIND). This research also was supported in part by a CHARM (Child Health Advances from Research with Mothers) small grant.