Gut Dysbiosis, Bacterial Colonization and Translocation, and Neonatal Sepsis in Very-Low-Birth-Weight Preterm Infants

Abstract

Gut dysbiosis may precede neonatal sepsis, but the association is still not well-understood. The goal of this study is to investigate the association between gut microbiota and neonatal sepsis, and to seek the evidence of colonization of pathogenic bacteria in the gut before evolving into an invasive infection. A prospective cohort study examined fecal microbiota composition in preterm infants with and without sepsis. Thirty-two very-low-birth-weight (VLBW) preterm infants and 10 healthy term infants as controls were enrolled. The fecal samples collected from the participants at the first, fourth, and seventh weeks of life underwent 16S rRNA amplicon sequencing for measurement of the diversity and composition of the microbiota. The bacterial isolates causing neonatal sepsis were genome sequenced. PCR was performed to confirm the translocation of the bacteria from the gut to the blood. The results showed that VLBW preterm infants with sepsis had lower microbial diversity in the gut at birth compared to preterm infants without sepsis and term infants. The composition of gut microbiome in preterm infants was similar to healthy terms at birth but evolved toward dysbiosis with increasing Proteobacteria and decreasing Firmicutes weeks later. The strain-specific PCR confirmed the presence of causative pathogens in the gut in 4 (40%) out of 10 VLBW preterms with sepsis before or at onset of sepsis, and persistence of the colonization for weeks after antibiotic treatment. The same bacterial strain could horizontally spread to cause infection in other infants. Prolonged antibiotic exposure significantly reduced beneficial Bifidobacterium and Lactobacillus in the gut. In conclusion, preterm infants with gut dysbiosis are at risk for neonatal sepsis, and the causative pathogens may be from the gut and persist to spread horizontally. The association of increased Proteobacteria abundance and decrease in microbiome diversity suggests the need for interventions targeting the gut microbiome to prevent dysbiosis and sepsis in VLBW preterm infants.

Keywords: dysbiosis; gut; microbiota; preterm infants; sepsis; very-low-birth-weight.

FIGURE 1

α-diversity and β-diversity of gut microbiota. α-diversity indices, including Chao1 (A) and Shannon index (B), and (C) β-diversity (CPCoA, covariate adjusted principal coordinates analysis) of gut microbiota of healthy term infants (HT), preterm infants without invasive infections (PNI), and preterm infants with invasive infections (PI). HT1, stool collected within the first week of age; PNI1 and PI1, stool collected within the first week of age; HT2, PNI2, and PI2, stool collected at 4 weeks of age; PNI3 and PI3, stool collected at 7 weeks of age. *p < 0.05; **p < 0.01; ***p < 0.001; ns, non-significant.

FIGURE 2

Abundances of bacterial taxa in different groups of the infants. Mean relative abundances of bacterial taxa at phylum (A) and genus (B) levels in each group of the stool collections. HT, healthy term infants; PNI, preterm infants without invasive infections; PI, preterm infants with invasive infections.

FIGURE 3

The main compositional proportion of gut microbiota and LefSe analysis. Phylum (A) and genus (B) levels for each group of participants expressed in heatmaps are shown. (C) The cladogram diagram shows the microbial species with significant differences in the three groups. Inside to outside showed the species classification at the level of phylum, class, order, family, and genus. The red, green, and blue nodes in the phylogenetic tree represent microbial species that play an important role in the PI1, PNI1, and PNI3 groups, respectively. Yellow nodes represent species with no significant difference.

FIGURE 4

α-diversity and β-diversity of gut microbiota. α-diversity indices, including Chao1 (A) and Shannon index (B), and (C) β-diversity (CPCoA, covariate adjusted principal coordinates analysis, CPCoA) of gut microbiota of healthy term infants at 4 weeks of age (HT2) and preterm infants with DOT lower than median (DOT_<median) and DOT higher than median (DOT_>median). *p < 0.05; **p < 0.01; ns, non-significant.

FIGURE 5

Abundances of bacterial taxa between preterm infants with different antibiotic exposure level. Mean relative abundances of bacterial taxa at phylum (A) and genus (B) levels in each group of the stool collections. HT2, healthy term infants at 4 weeks of age; DOT_<median, preterm infants with DOT lower than median; DOT_>median, preterm infants with DOT higher than median.