Gut microbiota in preterm infants receiving breast milk or mixed feeding.

Background: Preterm birth is the leading cause of mortality in newborns, with very-low-birth-weight infants usually experiencing several complications. Breast milk is considered the gold standard of nutrition, especially for preterm infants with delayed gut colonization, because it contains beneficial microorganisms, such as and .

Aim: To analyze the gut microbiota of breastfed preterm infants with a birth weight of 1500 g or less.

Methods: An observational study was performed on preterm infants with up to 36.6 wk of gestation and a birth weight of 1500 g or less, born at the University Hospital Dr. José Eleuterio González at Monterrey, Mexico. A total of 40 preterm neonates were classified into breast milk feeding (BM) and mixed feeding (MF) groups (21 in the BM group and 19 in the MF group), from October 2017 to June 2019. Fecal samples were collected before they were introduced to any feeding type. After full enteral feeding was achieved, the composition of the gut microbiota was analyzed using 16S rRNA gene sequencing. Numerical variables were compared using Student's -test or using the Mann-Whitney test for nonparametric variables. Dominance, evenness, equitability, Margalef's index, Fisher's alpha, Chao-1 index, and Shannon's diversity index were also calculated.

Results: No significant differences were observed at the genus level between the groups. Class comparison indicated higher counts of and in the initial compared to the final sample of the BM group ( < 0.011). In addition, higher counts of were detected in the final than in the initial sample ( = 0.040). According to the Margalef index, Fisher's alpha, and Chao-1 index, a decrease in species richness from the initial to the final sample, regardless of the feeding type, was observed ( < 0.050). The four predominant phyla were , and with being the most abundant. However, no significant differences were observed between the initial and final samples at the phylum level.

Conclusion: Breastfeeding is associated with a decrease in and and an increase of , contributing to the literature of the gut microbiota structure of very low-birth-weight, preterm.