Gastrointestinal function and microbiota development in preterm infants

Abstract

Functioning of the gastrointestinal tract, and of the microbiota residing therein, is of significance for nutrient digestion and absorption, pathogen resistance and optimal immune performance. During early life, development of the gut microbiota coincides, and affects, development of the metabolic, cognitive and immune system. Proper establishment of the gut microbiota is therefore considered essential for healthy development. In early life, the intestinal microbiota is relatively unstable and responsive to perturbations. Factors that are recognised to influence neonatal microbiota development include gestational age, delivery mode, nutrition and antibiotic use. As such, gut microbiota establishment is likely to be impacted in preterm infants, since they have an immature gut and are commonly exposed to caesarean section delivery, specific feeding regimens and antibiotic treatment. Although gut microbiota development can be negatively impacted during early life, the developing microbiota also provides an opportunity to be targeted as means of therapeutic strategy to support healthy growth and development. In light of this, it is important to understand how the preterm infant gastrointestinal tract is functioning, which microbes colonise, what the microbes are doing and how microbiota establishment is affected. In this thesis, gastrointestinal function and microbiota development during the early life of preterm infants, and the impact of various host and environmental factors on this development, were studied. The research described in this thesis was performed using material obtained during a single-centre, observational study including infants admitted to the neonatal unit born between 24-42 weeks gestation. A total of 238 infants (119 32 weeks gestation) were followed during the first six postnatal weeks, during which clinical factors were documented, and faeces and gastric aspirates were longitudinally collected for microbiota analysis. Microbiota development was not only approached compositionally via the application of qPCR and 16S rRNA gene amplicon sequencing, but also functionally via metaproteomics through LC-MS/MS, giving new insights into gut function and microbiota development in preterm infants. Via a metaproteomics approach, gestational age-specific developmental patterns of the preterm infant gastrointestinal proteome were identified. Gestational and postnatal age were associated with quantity of specific markers for gut function and maturation, as well as with composition of the gut microbiota. The faecal proteome of very preterm infants indicated a gut environment dominated by Bifidobacterium, and with better digestive capacity, compared to extremely preterm infants. We showed that a Bifidobacterium-dominated community is associated with increased proteins involved in carbohydrate and energy metabolism, including those involved in the degradation of complex carbohydrates like human milk oligosaccharides. Regarding preterm infants, who commonly experience protein deficits and growth retardation, further exploration of the gut microbiota’s metabolic traits is particularly relevant. The observed gestational age-specific developmental patterns were associated with the degree of exposure to perinatal antibiotics and respiratory support. Studying the sole effect of gestational age on gut microbiota development remains challenging due to the cohesion between gestational age and the degree of special care. Antibiotics are the most used therapeutics in neonatal intensive care units, prescribed for the prevention and treatment of infections and sepsis. It is important to understand the consequences of antibiotic treatment in neonates, as disturbances in microbiota development during this key developmental time window might affect early and later life health outcomes. We showed that two vancomycin dosages around time of removal of a central venous catheter presumably has no profound lasting effect on microbiota composition. However, postpartum amoxicillin/ceftazidime treatment impacts microbiota development, particularly by increasing the relative abundance of Enterococcus species, while decreasing Bifidobacterium abundance, during the first two postnatal weeks. In addition, more than five days of treatment seems to have a longer lasting effect on microbiota composition than less than three days of treatment as indicated by delayed (re)colonisation by Bifidobacterium species. In addition to gestational age and perinatal antibiotics, we included various factors during data analysis to elucidate their impact on gut microbiota development in preterm infants. As well as factors acknowledged for their influence on microbiota development, such as delivery mode and feeding strategy, we identified a potential influence of gender, respiratory support and maternal preeclampsia. These findings could serve as incentive for the initiation of future studies to unravel the true influence of such factors on microbiota development. The research described in this thesis contributes to current knowledge regarding gastrointestinal function and microbiota development during the early life of preterm infants and the factors associated with this development. This contribution could aid clinical practice and development of therapeutic strategies. In light of this, future work should consider 1) to implement functional analysis of the microbiota, 2) to study alternatives to antibiotics for the treatment and prevention of infections and 3) to elucidate the effect.