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Summary Host-Microbe Interactions
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Host-microbe interactionsLecture 1 – Microbial symbioses with humans
Are we one or are we many?
Functional significance of microorganisms colonizing our bodies
Human Microbiota= types of organisms present in an environmental habitat
organism itself
Human Microbiome= genome collection of microbes in a particular environmental
system, which refer to their function genome of organisms
The human microbiome is comprised of different microbiota that colonise different
habits of the body. Microbiota colonizing the skin is different from that of the gut.
The human body has different microbial habitats, we can’t live without microbiota.
The human body + commensal microbes = the superorganism. The human body has 10^12
cells and 10^4 genes, microbes contain 10^14 bacteria and 10^6 genes.
- Processing of nutrients
- Degradation of xenobiotics
- Protection from new microbes optimal fitness
- Regulation of epithelial homeostasis
Why is it important to know the human microbiota
- Development of biomarkers to predict predisposition to specific diseases
- Design of therapies targeting selected microbial species in particular body sites
- Personalized diet/drug therapies
- Tailor-made probiotics
How to identify the gut microbiota?
- Culturing? Majority of microorganisms cannot be cultured or enumerated using growth-
dependent approaches it’s too labor (arbeid) intensive + a lack of information
- 16S ribosomal RNA can be used for molecular profiling technologies for bacteria
- You have also group specific detection
Fusion of culture and molecular-based analyses
- The focus on molecular sequences in microbiome studies does not diminish the importance
of cultivation in the study of the human microbiome
, - The development of appropriate culture conditions for isolation is being guided by
metagenomic sequencing, which provides insights into the nutritional requirements of the
uncultured microorganisms.
Overview of the human microbiome
- There are currently integrated projects underway to answer basic questions about the
human microbiome
1. Do individuals share a core human microbiome?
2. Is there a correlation between the composition of microbiota colonizing a body
site and host genotype?
3. Do differences in the human microbiome correlate with differences in human
health?
4. Are differences in the relative abundance of specific bacterial populations
important to either health or disease?
Major microbial populations in the body sites sampled by human microbiome projects:
Belangrijk: Skin propion(i)bacterium. Saliva streptococcus. Urogenital tract lactobacillus.
Gastrointestinal tract bacteroides and firmicutes
Bacterial diversity of saliva see pwp.
In the saliva are aerobic bacteria.
With 16sRNA you can get aerobic and anaerobic bacteria.
Oral cavity and airways
- The oral cavity is a complex, heterogenous microbial habitat
- Saliva contains antimicrobial enzymes
- High concentrations of nutrients near surfaces in the mouth promote localized microbial
growth
- The tooth consists of a mineral matrix (enamel) surrounding living tissue, the dentin and
pulp.
Respiratory tract
- Microbes thrive in the upper respiratory tract
Bacteria continually enter upper respiratory tract from the air during breathing
Most are trapped in the mucus of the nasal and oral passages and expelled with
nasal secretions or swallowed and then killed in the stomach
, - Lower respiratory tract has no normal microbiota in healthy adults when microbes come
there it will cause disease
Ciliated mucosal cells move particles up and out of the lungs
Gastrointestinal microbiota
Humans are monogastric and omnivorous,
Microbes in the gut affect early development, health, and predisposition to disease,
Colonization of gut begins at birth. The difference starts whether If it’s a natural birth
or c-section
Gastrointestinal microbiota
The Stomach and Small Intestine
Small intestine: there is a high flow so absorption can take place, some microbes will
be washed away challenging for microbes to stay in the small intestine
The small intestine contains more aerobic bacteria since it is close to the oral cavity.
In the colon microbiota will digest carbohydrates into fatty acids.
4 types of epithelial cells: enterocytes, goblet cells (produce mucus), paneth cells and
enteroendocrine cells
There are no bacteria in the stomach, more when entering the small intestine.
The small intestine contain vili, large intestine doesn’t have vili.
Microbial populations in different areas of the GI tract are influenced by diet
and the physical conditions in the area.
The acidity of the stomach (~pH 2) prevents many organisms from colonizing
the GI tract; however, there is a rich microbiome in the healthy stomach.
Firmicutes, Bacteroidetes, and Actinobacteria are common in the gastric fluid,
while Firmicutes and Proteobacteria are common in the mucus layer of the
stomach.
Helicobacter pylori was discovered in the 1980s and has since been found in
~50 percent of the world’s population. When present, it is found in the gastric
mucosa.
Large intestinal microbiota see pwp.
The colon = for absorbtion of water, it has no vili, only crypte
, In the large intestine are mainly bacteroides and firmicutes
Intestinal microorganisms carry out a variety of essential metabolic reactions that
produce various compounds
The large intestine
The colon is essentially an in vivo fermentation vessel, with the microbiota
using nutrients derived from the digestion of food.
Most organisms are restricted to the lumen of the large intestine, while
others are in the mucosal layers. (Figure 24.6)
The vast majority (~98 percent) of all human gut phylotypes fall into one of three
major bacterial phyla: Firmicutes, Bacteroidetes, and Proteobacteria.
Individuals may have mostly Firmicutes, mostly Bacteriodetes, or a mix of the
two. This may regulate metabolism and the host’s propensity for obesity.
Urogenital tracts and their microbes
Altered conditions can cause potential pathogens in the urethra to multiply and
cause urinary tract infections
The vagina of the adult female is weakly acidic and contains significant amounts of
glycogen.
Lactobacillus acidophilus ( keeps the pH low), a resident organism in the vagina,
ferments the glycogen, producing lactic acid.
Lactic acid maintains a local acidic environment.
Vaginal bacterial diversity see pwp
It is less diverse than gastrointestinal tract
The skin and its microbes quite diverse, comes after gastrointestinal tract
There are approximately 1 million resident bacteria per square centimeter of skin for
10
a total of about 10 skin microorganisms covering the average adult.
The skin surface varies greatly in chemical composition and moisture content
Three microenvironments: Dry skin, moist skin, sebaceous skin (oily)
Composition is influenced by: environmental factors (weather), host factors (age,
personal hygiene)
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