MHD7 Gut microbiota and aging Flashcards
How many different types of species are there in a human faeces sample?
Roughly 160
When is the host microbiome most malleable?
in early life and in late life
Is the gut of the foetus sterile before birth?
The gastrointestinal tract has long been thought to be sterile at birth with bacterial colonisation beginning during the delivery process (from the maternal faecal or vaginal microbiota and/or the environment). However, researchers have found evidence of bacteria in the placenta, amniotic fluid and meconium (first stool that forms in a foetus in utero).
Other scientists argue that this is due to contamination
Define kitome
Contaminants from the DNA-extraction kits.
What is the difficulty when testing placental samples for microbial signal?
Placental microbial signal is likely to be weak and difficult to distinguish from the background microbial signal.
During which period is inter-individual variation in the microbiota reduced?
Two to three years after birth the human gut undergoes a rapid and dynamic period of colonisation. Bacterial diversity increases.
Which community-type will the gut microbiota of a vaginally-delivered baby resemble at birth?
Vaginal
Which community-type will the baby’s gut microbiota resemble at 27 months?
Feacal
What are the two significant transitions that the establishment of a stable gut microbiota generally accompany? Explain these
1) The first transition occurs soon after birth during lactation. Initial bacteria to colonise the large gut are facultatively anaerobic strains such as Escherichia coli and streptococci. These first colonisers metabolise any traces of oxygen in the gut reducing the environment into one of strong anaerobic conditions. Once this anaerobic environment is created a range of selection pressures shape the colonisation trajectory of the gut.
2) The second transition occurs during the weaning period, with the introduction of solid foods and continuation of breast milk feeding. Following this transition an adult-type complex microbiome takes shape dominated by the phyla Bacteroidetes and Firmicutes.
What is the early-life microbiota of infants born vaginally dominated by?
Lactobacillus, Prevotella, or Sneathia
Infants born by caesarean section have an intestinal microbiota more consistent with what?
the skin microbiota. This is dominated by Staphylococcus, Corynebacterium, and Propionibacterium. Environmental factors (e.g. air, healthcare workers, delivery and surgical equipment) also appear to have a greater effect on the microbiota of infants born by caesarean section.
What does caesarean birth have an associated increased risk of?
Immune disorders such as allergic rhinitis, asthma, and celiac disease
How do Human milk oligosaccharides (HMOs) reach the colon?
HMOs are a major component of breast milk and include oligosaccharides such as galactooligosaccharide (GOS). These HMOs are only partially degraded in the small intestine and so reach the colon
What effect do HMOs have on the colon?
They have a probiotic effect, selectively stimulating the development of a Bifidobacterium-rich microbiota (referred to as “Bifidus flora”).
How are HMO broken down in babies?
The bifidobacteria ferment these oligosaccharides to produce short chain fatty acids.
What is the difference in gut microbiota of infants fed on breast milk versus formula milk?
Formula-fed infants develop a complex microbiota with higher proportions of facultative anaerobes, such as Bacteroides and Clostridia, than breast-fed infants who are colonised more commonly by aerobic organisms. Breast milk also contains numerous factors that modulate and promote the maturation of the immune system, which in turn can select the bacteria that colonise the gut. The faecal microbiota of breast-fed infants exhibits more dramatic changes in composition over their first year of life. Breast milk has also been found to contain members of the Lactobacillus, Streptococcus, Enterococcus, Peptostreptococcus, Staphylococcus, Corynebacterium, and Escherichia species
The use of antibiotics is ____ prevalent in pre-term and caesarean babies
more
In infants, antibiotic exposure shifts the gut microbiota towards a high abundance of what types of bacteria? What other impact does it have on the microbiota?
Proteobacteria and low abundance of Actinobacteria populations.
It also reduces the overall diversity of the infant microbiota and selects for drug-resistant bacteria.
Exposure to broad-spectrum antibiotics for the first four days of life has been shown to do what to the infant’s microbiota?
Reduce colonisation by Bifidobacterium and increase colonisation by Enterococcus. In these infants, an overgrowth of Enterobacteriaceae and Enterococcus was seen by one month of life.
Epidemiological studies have found an association between early-life antibiotic intake and an increased risk for what diseases?
type 1 diabetes, asthma, atopic disease and eczema
What other factors are proposed to affect the early-life development of the microbiota?
Host genetics Composition of the maternal microbiome Length of gestation Birth environment Hygienic practices
What are the main factors that influence childhood gut microbiota?
geography and dietary habits
What is the basic difference between the gut microbiota of children vs infants?
The microbiome of children is more stable than that of the infant and has less variability across individuals.
What is the difference in faecal microbiome of children from USA vs Bangladesh?
Bangladeshi children were found to have higher bacterial diversity and possess communities dominated by Prevotella. In contrast, the US children had less diversity and a community dominated by Bacteroides and Firmicutes.
What is the difference in faecal microbiota between children from central Asia and South East Asia vs children from Eastern Asia?
What may be part of the reason for this?
Central Asia and South East Asia: Prevotella-dominated (P-type) microbiota
Eastern Asia: Bacteroides-Bifidobacterium-dominant (BB-type) microbiota
Diet
What is the difference in faecal microbiota between rural and urban populations?
Rural: P-type microbiota
Urban: BB-type microbiota
What may be the reason for the different P-type/BB-type microbiota?
Modernisation of the foods was associated with these differences with the urban children (BB-type) consuming a high-fat diet compared to those from the rural setting (P-type). The BB-type microbiome was enriched with genes encoding bile acids that aid in lipid absorption and the P-type microbiome was enriched for genes involved in oligosaccharide-degrading enzymes involved in plant digestion.
