Impact of donor human milk pasteurization methods on the gut microbiome of preterm infants

Abstract Background Preterm infants are often fed donor human milk (DHM) when the mother’s own milk is insufficient or not available. Holder or Retort pasteurization is used to inactivate potential pathogens in DHM. The effects of DHM pasteurization methods on the infant gut microbiome are unknown. Methods To compare the gut microbiome and clinical outcomes between preterm infants fed Holder- versus Retort-pasteurized DHM, we performed weekly collections of stool samples from infants born <34 weeks’ gestation and/or <1500 g birth weight. We analyzed stool samples from 150 patients exclusively fed DHM [Retort (n = 80), Holder (n = 54)] or exclusively fed mother’s own milk (n = 16). Whole-metagenome sequencing was performed to assess microbiome composition, diversity, and functional enrichment. Results Compared to infants fed Retort-pasteurized DHM, infants fed Holder-pasteurized DHM showed higher alpha-diversity (Chao-1 p = 0.007) and a higher abundance of beneficial anaerobes, such as Bacteroides thetaiotaomicron, Clostridium spp., and Bifidobacterium spp. Functional enrichment analysis revealed significant differences in carbohydrate metabolism, transport systems, and regulatory pathways between feeding groups. There were no statistically significant differences in short-term clinical outcomes, such as necrotizing enterocolitis, length of hospitalization or death. Conclusion Differences in pasteurization methods for DHM resulted in measurable gut microbiome changes in preterm infants. Impact It is known that the preterm infant gut microbiota is different in infants fed pasteurized donor milk compared to mother’s own milk. However, the impact of different pasteurization methods for donor milk on the infant gut microbiome is unknown. We show that the type of pasteurization of donor human milk influences the gut microbiome and its function in preterm infants. In contrast to feeding Retort-pasteurized donor human milk, feeding Holder-pasteurized donor human milk generates an infant gut microbiome similar to feeding mother’s own milk.