The Gut Bacterial Flora - Focus on Early Life and Physiological Traits

Abstract: The gastrointestinal tract of the foetus is considered sterile but during vaginal birth the neonate comes into contact with bacteria from the maternal vaginal and intestinal microbiota. The main focus of this doctoral thesis was to elucidate the initial bacterial ecosystem in newborns and to relate microbial perturbations to physiological traits. The bacterial flora was mainly studied with molecular-genetic methods. When the microbiota was assessed in one-week-old infants, reduced faecal bacterial diversity was found in infants developing atopic eczema at the age of 18 months compared to those infants not developing eczema. To further elucidate the pioneer microbiota, stool samples from healthy full-term vaginally-born neonates was studied. Lactobacillus was found in all newborns within 48 hours after birth. Species commonly found in the vaginal microbiota were to some extent detected among the babies. Other bacterial groups were found in varying prevalence. Interestingly, a subgroup of neonates born large for gestational age had significantly more Proteobacteria compared to neonates born appropriate for gestational age. Maternal microbiota and dietary habits are known to impact offspring physiology. Results presented in this thesis show impaired physiology in suckling rat pups to dams of the outbred Sprague-Dawley stock when these were treated with high-energy dense diet during the gestation and lactation period. Offspring body weight, adiposity, gut permeability and systemic inflammation were further accentuated if the Gram-negative Escherichia coli was given to the dams in combination with the high-energy dense feed. In a similar experimental design, the pups were monitored in a longitudinal study. E. coli exposure from foetal life until six months of age decreased the diversity of the caecal microbiota along with enhanced adiposity. In contrast, when the Gram-positive Lactobacillus plantarum was given instead of E. coli, body weight gain and fat accumulation were lower in addition to a more favourable gut microbiota, implying the prospect of effect on health homeostasis by bacterial consumption. This thesis suggests that a high load of E. coli should be avoided in pregnant mothers and in children, and treatment with L. plantarum may be a therapeutic option. However, more extensive research is needed to establish the relationship between inflammation, obesity and the bacterial flora of the gut. A general conclusion concerning the microbiota is that the intestinal ecosystem should be studied at least at the hierarchical level of genus or family, but preferably on the species level since looking at the phylum level can give superficial information.