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Summary lectures Host-microbe interactions
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HOST- MICROBE INTERACTIONSLECTURE 1 | MICROBIAL SYMBIOSES WITH HUMANS [11/11/2019]
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.
Human microbiota= Types of organisms present in an environmental habitat.
Human microbiome= Genome collections of microbes in a particular environmental system, which
refer to their function. a
The superorganism= Self + Commensal microbes (Human/gut microbiota)
- Functions
▪ Processing of nutrients
▪ Degradation of xenobiotics
▪ Protection from new microbes
▪ Regulation of epithelial homeostasis
- Importance
▪ 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.
- Identifying the Mircobiota
1. Sequencing; 16s ribosomal RNA
- Types
o Molecular profiling technologies
- Subtypes
a) DGGE
b) Phylogenetic chip
c) Barcoded Pyrosequencing
o Group specific detection
- Subtypes
a) FISH/FACS
b) qPCR
- Attributed Disorders
▪ The role of the gut microbiota in obesity; Mouse models
o Normal mice have 40 percent more fat than germ- free mice with the same diet.
When germ-free mice were given normal mouse microbiota, they started gaining
weight.
o Mice that are genetically obese have different microbiota than normal mice. Obese
mice have more Firmicutes.
o Like the mouse model, obese humans have more Firmicutes than non-obese
humans.
o The nature and transferability
of gut microbiota is dependent
on diet as well as genetics.
, ▪ Dental Caries and Periodontitis
o Cells form a biofilm called dental plaque, which has Streptococcus and other
fermenting bacteria. (Figure 24.21)
o These fermenters produce acid, which wears down the tooth enamel.
o Periodontal disease is thought to contribute to several systemic conditions, including
cardiovascular disease and arthritis.
- Antibiotics
▪ Oral antibiotics decrease ALL microbes in the human gut (both target and non-target).
▪ Use of antibiotics during the first few months of life increases the risk of developing
inflammatory bowl disease and other disorders related to dysbiosis.
▪ Clostridium difficile infections are associated with antibiotic use.
- Characteristics
o Clostridium difficile is a spore-former and generally
antibiotic resistant.
o A newer therapy for Clostridium difficile infection is a
fecal transplant.
- Probiotics and Prebiotics
▪ Probiotics= Life organisms that confer health benefit to the
host.
- Characteristics
o Species of Bifidobacterium and Lactobacillus bacteria are commonly used probiotics
found in yogurt and probiotic drinks. (Figure 24.24)
o They may work by taking up space or nutrients, limiting the ability of pathogens to
colonize the gut.
▪ Prebiotics= Typically carbohydrates that are indigestible by human hosts, but provide
nutrition for fermentative gut bacteria.
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?
,Oral cavity and airways
- Characteristics
▪ The oral cavity is a complex, heterogeneous
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
- Characteristics
▪ Microbes thrive in the upper respiratory tract.
o Bacteria continually enter upper
respiratory tract from the air during
breathing.
o 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.
o Ciliated mucosal cells move particles up and out of the lungs.
Gastrointestinal microbiota
- Characteristics
▪ Humans are monogastric and omnivorous
▪ Microbes in the gut affect early development health, and predisposition to disease.
▪ Colonization of gut begins at birth.
▪ Intestinal microorganisms carry out a variety of essential metabolic reactions that produce
various compounds.
- Microbiota
▪ The Stomach and Small Intestine
- Characteristics
, o Microbial populations in different areas of the GI tract are influenced by diet and the
physical conditions in the area.
o 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.
o Firmicutes, Bacteroidetes, and Actinobacteria are common in the gastric fluid, while
Firmicutes and Proteobacteria are common in the mucus layer of the stomach.
o 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.
o pH 4-5
o Aerobic bacteria= They can live in the present of
oxygen.
▪ Large intestinal
- Characteristics
o The colon is essentially an in vivo fermentation vessel,
with the microbiota using nutrients derived from the
digestion of food.
o Most organisms are restricted to the lumen of the large
intestine, while others are in the mucosal layers.
o Different microenvironments in the large intestine.
o pH 7
o Anaerobe bacteria= They can’t live in the present of
oxygen.
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.
Urogentical tracts
- Characteristics
▪ Altered conditions can cause potential pathogens in the urethra (e.g. Escherichia coli and
Proteus mirabilis) to multiply and cause urinary tract infections.
▪ The vagina of the adult female is weakly acidic and contains significant amounts of glycogen.
▪ Lactobacillus acidophilus, a resident organism in the vagina, ferments the glycogen,
producing lactic acid.
▪ Lactic acid maintains a local acidic environment.
The skin
- Characteristics
▪ There are approximately 1 million resident bacteria per square centimeter of skin for a total
of about 1010 skin microorganisms covering the average adult.
▪ The skin surface varies greatly in chemical composition and moisture content
- Types of Microenvironments
o Dry skin
o Moist skin
o Sebaceous skin (oily)
▪ Composition is influenced by;
o Environmental factors (e.g., weather)
o Host factors (e.g., age, personal hygiene)
o Each microenvironment shows a unique microbiota.
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