Module 11- 210

Host-Microbe Interactions

What is microbiome

Community of microorganisms plus their environment and collective genes

What is a microbial community

Has distinct properties and functions and its interaction with its environment resulting in the formation of specific ecological niches

What is microbiota

The living microbial members

Roles of the microbiota

Trains the immune system

Provide nutrition and protection

Rank the body sites based on their microbiota diversity and abundance:

Intestinal tract

Skin

Blood

How does the skin microbiome vary

By moisture, sebum, and exposure

What are the sebaceous glands dominated by

Propionibacterium species

Where it is moist (on the bends of elbows and feet) parts of the skin dominated by

Staphylococcus and corynebacterium

What are the dry spots of the skin dominated by

More diverse

includes beteproteobacteria and flavobacteriales

Some fungi like malassezia are across the skin

The gastrointestinal tract of humans

Monogastric with a omnivorous diet

Colonization of gut begins at birth and is shaped by delivery mode, diet, and antibiotics

Diverse microbial cells 10^13

Functions in digestion, vitamin synthesis, immune modulation, and colonization resistance

The gradients in pH and oxygen and nutrients define the niches

The stomach microbiota

Low pH of 2 limits diversity but still hosts acid tolerant taxa

Low biomass but metabolically active and contributes to hormone signalling and immunity

Common groups: firmicutes, bacterioidetes and actinobacteria and propionbacterium

What is helicobacter pylori

Discovered in the 1980s

Colonizes mucose in about 50% of people; can cause gastritis and peptic ulcers which can now be cured with antibiotics

Acid-resistance

Large intestine/colon microbiota

Intestinal microorganisms carry out a variety of essential metabolic reactions that produce various compounds

The colon is an in vivo fermentation chamber; microbiota use nutrients from the digestion of food

Anaerobes dominate such as bacteroids, clostridia, and faecalibacterium

Functions of the gut microbiome

Breaks down complex carbs and fibres that digestive system alone cannot process

Helps educate the immune system to differentiate between harmful pathogens, beneficial microbes, and self

Synthesizes certain vitamins like B and K which can be absorbed and utilized by human host

Role in maintaining the integrity of the gut epithelial barrier, preventing leaky gut and the translocation of harmful substances into the bloodstream

Serves as a barrier against harmful pathogens by occupying ecological niches and competing for resources

Respiratory tract microbiome

Microbes thrive in the upper respiratory tract

Bacteria continually enter the upper respiratory tract from the air during breathing

Many are trapped in the mucus of the nasal and oral passages and expelled with nasal secretions or swallowed and then killed in the stomach

Mucus, cilia and immune defences maintain blance

Dysbiosis may precede infections

The upper respiratory tract microbiota vs the lower respiratory tract

Upper tract is diverse but dominated by streptococcus, corynebacterium, and moraxella

Lower tract has a low biomass but is not sterile and include transient species but there’s no normal microbiota in healthy adults

Only smaller particles then 10 millimetres in diameter reach the lungs

The oral microbiome

The oral cavity is complex heterogeneous microbial habitat

Cone of body richest microbiomes

Saliva contains antimicrobial enzymes and provides nutrients

Biofilms formed on the teeth, gums, tongue, and tonsils

Oral gut axis is where the swallowed microbes seed gut communities

Dental plaque biofilm formation

S. mutans produces a glucan matrix which leads to the biofilm formation and colonization by taxa which could not have bound the tooth surface unassisted

Acid with the biofilm selects acid-tolerant cariogenic organisms like S. mutans, Lactobacillus spp, and veillonella spp

If it goes uncheck it can destroy the protective enamel coating of the tooth leading to clinical disease

Urogenital microbiomes

Urinary tract has a generally low biomass the flushing by urine limits colonization

Urethral and virginal microbiomes differ sharply by sex and hormones

Dysbiosis produces UTIs, vaginitis, and infertility issues

Vaginal microbiome

Varies and can change in composition leading to dysbiosis of the normal microbiota and can be associated with inflammatory infection

Its weakly acidic and contains a significant amount of glycogen; the lactobacillus acidophilus ferments the glycogen which produces lactic acid

The lactic acid maintains the local acidic environment

G. vaginalis is a case of bacterial vaginosis

Male genital tract microbiome

Has a low biomass

Ecosystem with relatively diverse bacterial communities, dominated by skin and urethral taxa

Semen microbiota may influence fertility and pregnancy outcomes

Koch postulates were critical in establishing the germ theory of disease. What scenarios fulfill the kochs postulates as originally intended but are explained but the modern understanding of germ theory of disease

The patients lie in a highly polluted environment that their ability to combat infectious diseases

The patients have an underlying conditions and are prone to opportunistic factors

The bacterium is impossible to grow in the lab and cannot be isolated but is detectable using molecular tools

What happens during Koch postulates

A pathogenic strain carrying certain gene-isolate to find out and transform it to a non-pathogenic strain to test to a see if there has been a gain of function of a pathogenic strain

You are trying to fulfill Kochs postulates for a project. As described in the experiment, you isolate a probable bacterial pathogen from an animal with diarrhea and you infect healthy animals with this newly isolated bacterium. The newly infected animals do not develop the disease why

The disease was not caused by this bacterium

The gut microbiota protected the animal

You did not isolate a pathogenic bacterium

You fulfill the first molecular postulate by identifying a genomic island in a pathogenic E. coli that is absent in a virulent E. coli. What fills the remaining molecular Kochs postulate

Multiple steps are needed

Removing the genomic island from the pathogenic E. coli results in a decrease in virulence in a mouse model

Add back the genomic island into the E. coli restores virulence in a mouse model

or remove the genomic island from the pathogenic E. coli results in a decrease in virulence in a mouse model and adding the genomic island into a virulent E. coli results in a increase virulence in a mouse model

What is a pathogen

A microorganism that causes disease or tissue damage in a host

What is a primary pathogen

Can cause disease in a healthy host, regardless of the hosts immune system or resident microbiota

What is a opportunistic pathogen

Causes disease only when normal host defence are impaired

What is pathogenicity

The ability of a microorganism to cause disease/ inflict damage on the host

What is virulence

The relative ability of a pathogen to cause disease. A measure of pathogenicity or degree of pathogenicity

What are virulence factors

Are toxic or destructive substances produced by the pathogen that directly or indirectly enhance invasiveness and host damage by facilitating and promoting infection

What is infection

Establishment and growth of a microorganism in a host with or without harm

What is disease

Damage or injury to the host that impairs host function

How can violence be measured

Can be estimated from experimental studies of the lethal dose 50 which is the amount of an agent that kills 50% of the animals in a test group

What is an infective dose

The minimum number of organisms required to cause an infection in a host

Can vary depending upon route of entry, age, health, immune status, and environmental factors

Does not correlate with disease severity

Entry and exit of pathogens

Not all contacts with pathogens result in disease but they must gain access and overcome several barriers

Mucosal surfaces are important portals of entry

Most have specific entry points and some pathogens can cross the placental barrier

What are the steps of microbial virulence

Adherence to colonization to invasion to damage

Neisseria meningitis and neisseria gonorrhea process Type I pili and these are important virulence factors. Based on your knowledge of pili, what is the role the pili during the infection

Act as adhesin for the attachment phase

What is adherence

A pathogen must usually gain access to host tissues and multiply before damage can be done

Enhanced ability of microbes to attach to host tissues; its necessary but not sufficient to start disease

What are adhesins

Are glycoproteins or lipoproteins found on the pathogens surface that enable it to bind to host cells

N. gonorrhoeae adheres to mucosal epithelial cells using the opa protein and pilli

Adherence of fimbraie

Fimbriae are cell-surface proteins that function as adherence factors and allow attachment to epithelial surfaces

Fimbraie are common in many gram-negative bacteria and some gram positive

Within a species like E. coli and some strains produce multiple types of fimbraie and some produce only one and others produce none

Bacteria lacking fimbraie are less likely to adhere effectively to surfaces and host cells which make them non-pathogenic or less virulent

Adherence of capsules

Capsules are dense polymer layers (usually polysaccharides) surrounding the cells that are not covalently attached to the bacterium but function in adherence to host tissues and to other bacteria and attach to specific host receptors

In S. pneumoniae capsules prevent destruction of the bacterium by phagocytes and are essential for pathogenicity; are antiphagocytic; produce pollysaccharide capsule

Adhesins in afimbrial

In N. gonorrhoeae Opa surface protein binds to CD66 host protein found only on the surfaces of urogenital epithelial cells

Pili are also used for attachment to epithelial cells and has several nonfimbrial adhesins

What is colonization

The growth of microorganisms after they’ve gained access to host tissues without causing disease

Starts with mucous membranes or tightly packed epithelial cells coated in mucus, a thick secretion of glycoproteins- formation of biofilm

Infection is once the microbes invade tissue and cause damage

When does an infection become a disease

When a microorganism that is established and growing in a host causes damage and injury that impairs host function

Pathogenic factors

Toxins, capsules, siderophores, secretion systems, motility, and biofilm formation

Host factors

Immune status, microbiota composition, age, nutrition, genetic susceptibility

Environmental factors

Stress, temperature, pH, antibiotics, and nutrient limitation

Transmission and persistence

Mode of spread, host reservoir, and environmental survival

What are SPIs

Distinct genomic regions that contain clusters of gene responsible for virulence

Clusters are often located on the bacterial chromosome, plays a crucial role in enabling Salmonella to infect and cause disease in humans and animals

Usually acquired through horizontal gene transfer

What is SPI 1

Invasion of host cells. Has a T3SS for injection of proteins that manipulate host cell functions to promote bacterial entry

What is SPI 2

Involved in survival and replication in host cells such as macrophages. Contains a second T3SS for the manipulation of intracellular environments, allowing the bacteria to avoid immune system detection

What is the compromised host

Has a reduced resistance to the infection

Caused by smoking, stress, sleep deprivation, genetic immune defects, ect

Why do enzymes and toxins matter

Understand how microbes damage and manipulate host

Identify targets for drugs and vaccines

Disease prevention, food safety, and infection control

Connect molecular microbiology to human disease and global health

How do enzymes work as virulence factors

Break down tissues and access nutrients

Promote the spread and deeper tissue invasion

Aid anaerobes in access

What is coagulase

Used by pathogens like staphylococcus aureus to form a insoluble fibrin layer around them, enabling clot formation and protection from attacks from host cells

What is streptokinase

Pathogens like streptococcus pyogenes use it as a fibrinolytic enzyme that dissolved fibrin clots permitting dissemination

What are antibody proteases

Antibodies normally binding to antigens on the surface of pathogenic bacteria. Phagocytes then bind to the antibody which initiating phagocytosis

Some bacteria produce proteases, virulence factors that break down host antibodies to evade phagocytosis

What are exotoxins

Toxic proteins released from the pathogen as it grows

3 categories:

cytolytic toxins that disrupt the membrane

AB toxins

Superantigen toxins

What is toxicity

Ability of microorganism to cause disease as a result of a performed toxin that inhibits host function or kills host cells

What are cytolytic exotoxins

Work by degrading cytoplasmic membrane integrity, causing cell lysis and death

Toxins that lyse red blood cells are called hemolysins

What are pore-forming cytotoxin

Typically exist as soluble monomers that bind to the membrane and then oligomerize which forms a ring structure to create a transmembrane pore

The pores allow the uncontrolled influx of ions, leading to the cell swelling and lysis

What are AB exotoxins

Consists of 2 subunits A (active) and B

Work by binding to host cell receptor (B subunit) and transferring damaging agent (A subunit) across the cell membrane

What is diphtheria exotoxin

Block protein synthesis

Produced by Corynbacterium diptheriae which is a type of actinobacteria

AB toxin that is made up of active domain and a binding domain. The A domain adds an ADP-ribosyl group to EF-TU which prevents its function in translation

The diphtheria toxin coded by a lysogenic phage B

What is phage conversion

Conversion of nonpathogenic strain to toxigenic and pathogenic by infections with B

What other toxins inhibit protein synthesis or are AB toxins

P. auruginosa- exotoxin A

Shiga toxins- S. dysenteriae

Shiga-like- enterotoxigenic E. coli

Botulinum and tetanus

Clostridium tetani and clostridium botulinum produce potent AB exotoxins that effect the nervous tissue

Botulinum toxin consists of several related AB toxins that are the most potent biological toxins known

Tetanus toxin is also an AB protein neurotoxin

What are enterotoxins

Activity effects the small intestine

Cause massive secretion of fluid into the intestinal lumen which causes vomiting and diarrhea

Cholera enterotoxin

AB-type exotoxin produced by vibrio cholerae (the causative agent of the waterborne disease cholera)

Affects the small intestine

Massive secretion of fluid into the intestinal lumen causing vomiting and diarrhea and maybe death

AB enterotoxins

Shigella and salmonelle are also AB enterotoxins that inhibit protein synthesis tho

E. coli enterotoxins

Shiga-like

Superantigens entertoxins

S. aureus

Bypass normal immune checks activating huge numbers to T-cells which can lead to cytokine storm which causes shock

What are endotoxins

The LPS portion of the cell envelope of certain gram-negative bacteria which is a toxin when solubilized

Lipid A is the toxic portion

Less toxic then exotoxins

Presence can be detected by the limulus amoebocyte lysate assay