W20 Microbe host interactions

Question 1

Define Symbiosis: !
What are the 3 symbiotic relationships?

Answer 1

=Close interaction between two organisms of different species

• Mutualism
• Commensalism
• Parasitism

Question 2

What is Mutualism?
What is an example?

Answer 2

=BOTH species (bacteria and host) BENEFIT from their interactions

E.g.: Many hundreds of bacterial species living in the gut (gut microbiota/flora)
-The human gut harbours trillions of microbes in healthy conditions

Benefit to the bacteria=They have a place to eat, survive and multiply
Benefits to the human=Bacteria aid digestion, breaking down food that the host cannot normally digest and producing vitamins (such as B and K)

Question 3

Define Commensalism:
What is commensal bacteria?
What is an example?

Answer 3

ONE partner in the relationship benefits.
The other neither benefits nor is harmed.

Example: Commensal bacteria colonise epithelial surfaces of skin
1 million bacteria on each square centimeter (cm2)
Benefit to the bacteria =Acquire nutrients consuming dead skin and a place to live and grow

Commensal bacteria may become pathogenic and cause disease

Question 4

What is Parasitism? (relationship)
Example of a parasite?

Answer 4

One partner, the pathogen, HARMS the host, causing infectious disease

Example: SARS-CoV-2 infects human cells of the respiratory system, causing COVID-19.
Benefit to the virus=Virus takes advantage of the translational machinery of the cell to replicate (multiply) virus particles.

Viruses are defined as obligate intracellular parasites
Harm for the human cells= Viral infections lead to the death of the cells and tissue damage

Question 5

Define Microbiota: !

Answer 5

All the microorganisms that live in and on an organism.

Human microbiota
 Approximately 10^11 organisms
 1-3% total body mass
 Generally non-pathogenic
 Symbiotic with host
Cells comprising human body: 90% microbes, 10% human cells

Question 6

Early Colonisation of Microbiota:
(for info)

Answer 6

• Microbiota begins developing at birth
• Vaginal birth provides exposure to
  microbes from the mother’s birth canal, whereas caesarean delivery provides microbe exposure from initial caretakers.
• Bifidobacteria are important colonisers of the gut -Can ferment sugars found in human breast milk providing the infant with calories and lowers the gut pH, limiting growth of pathogens.

Question 7

Dynamic and diverse microbiota composition: (!)
When does a human have a complete microbiota composition?

Answer 7

• Microbiota is not static
• It reach an adult-like composition by age 3
• Relative stable in adult ages without any major physical or lifestyle changes (diet, stress, antibiotic therapy)
• Variable from person to person and at different sites within a person
• Not only bacteria. Some archaea, fungi, and viruses are also present

Question 8

Name some Human microbiota body sites (!)
Which areas of the body are free of microorganisms?

Answer 8

Mouth, Lungs, Skin, Urogenital tract, Large
Intestine, Eyes Nose and throat, Stomach,
Small intestine

Internal organs and tissues (that is, brain, blood, cerebrospinal fluid, muscles) are normally free of microorganisms

Question 9

Distribution and composition of normal
microbiota are determined by which factors? (4)

Answer 9

• Nutrients
• Physical and chemical factors
• Host defenses
• Mechanical factors

Question 10

Name some Human microbiota functions: (!)

Answer 10

1. Dietary fibre fermentation (resistant to host enzymes) into Short Chain Fatty Acids (source of energy)
2. Synthesise and excrete vitamins (vit. K and B12)
3. Prevent .colonisation by pathogens
   -Competitive exclusion of pathogens
   -Production or stimulation of antimicrobial molecules
4. Stimulate the development of certain tissues (intestines, lymphatic tissues, capillary density)
5. Immune system stimulation/maturation
6. Regulate inflammation
7. Modulate and affect the central nervous system (Gut-Brain Axis)

Question 11

What is Dysbiosis? (!)
What can it lead to?
What can it be caused by?

Examples?

Answer 11

=An imbalance of microbial species and a reduction in microbial diversity within certain bodily microbiomes
*Can lead to a variety of diseases that involve inflammation
*Dietary changes, antibiotic use, psychological and physical stress

e.g. IBS, Diabetes, Obesity, Rheumatoid arthritis

Question 12

What can Fatty acids to do fatty acetyl coA?

Answer 12

Can convert into Fatty acetyl CoA and undergo Beta oxidation (4 steps) to produce Acetyl coA so it can enter the Krebs cycle

Question 13

What are Opportunistic infections? (!)

Answer 13

• An opportunistic infection - infection caused by commensals (part of the normal microbiota) that do not cause generally disease in a healthy host but in some circumstances can become opportunistic pathogen:
• Dysbiosis – altered microbiota
  -The opportunistic pathogen can outgrow
• Immunocompromised patients

Question 14

What are Probiotics? (!)

Answer 14

Live microorganisms, which, when administered in adequate amounts, can restore the normal balance of microbiota (especially in the gut and genital) and related beneficial functions, conferring a health benefit to the host.

Question 15

What are Prebiotics?!

Answer 15

Compound(s) added to enhance the colonisation and positive health benefits of probiotic microbes.

Question 16

What are Synbiotics?!

Answer 16

Foods or supplements that include both a prebiotic and a probiotic.

Question 17

Define an Opportunistic pathogen: (!)

Answer 17

May be part of normal microbiota and causes disease when the host is immunocompromised or when they have chance to outgrow

Question 18

Define Pathogenicity:

Answer 18

Ability of a pathogen to cause disease

Question 19

Define Virulence:

Answer 19

Degree of harm (pathogenicity) inflicted on its host.

Question 20

What are the steps in pathogenesis of bacterial infections? (6)

Answer 20

1. Entry of pathogens into the body*
2. Attachment of the pathogen to some tissues
3. Multiplication
4. Invasion/spread of the pathogen
5. Evasion if the host defences/immunity
6. Damage to the host tissue(s)

*Any organism that causes disease according to the transmission routes (e,g. penetration, inhalation, ingestion and introduction into the blood)

Question 21

What occurs in Entry, adherence and colonisation? (!)

Answer 21

1. Entry into the host
   -Portal of entry
   -Skin, respiratory, gastrointestinal, urogenital
   systems, or conjunctiva of eye
2. Attachment of microbe to specific target cells (highly specific and permanent or nonspecific and reversible)
   -Adherence structures:
   -Pili
   -Fimbriae
   -Glycocalyx (Capsule)
3. Colonisation—establish a site of microbial replication on or within host

Question 22

Define invasiveness
What are the 2 types?

Answer 22

= Ability to spread to adjacent tissues

4. Invasion (active or passive)
    Active - occurs through production of lytic substances that alter host tissue
   E.g. pathogens that induce the disruption of the intestinal lining

 Passive – host tissue alteration was already present and it was not
caused by the pathogen
skin lesions, insect bites, wounds

Question 23

Invasion - examples

Answer 23

• Once under mucous membrane, a pathogen can penetrate deeper
  tissues.
   Bacteremia—presence of viable bacteria in the blood
   Septicemia—bacterial or fungal toxins in the blood.
• Invasion varies among pathogens:
   Clostridium tetani (tetanus) is noninvasive because it does not
  spread from one tissue to another, but toxins become blood borne
   Bacillus anthracis (anthrax) and Yersinia pestis (plague) also
  produce toxins and are highly invasive
   Streptococcus span invasiveness

Question 24

Define: Overcoming Host Defences
Examples?

Answer 24

=Successful pathogens overcome
competition and elude initial host responses as well as the adaptive immune system:

 Find shelter to avoid recognition by defence cells.
 Survive and replicate inside host cells
 Squeeze between host cells.
 Avoid phagocytosis (capsule)
 Burrow under mucus.
 Find shelters within biofilms.
 Produce enzymes that inactivate innate resistance mechanisms.
 Excrete specialized proteins to selectively kill host cells
 Mutate and/or reduce cell surface proteins detected by immune cells

• Bacteria such as Streptococcus pneumoniae, Neisseria
  meningitidis, and Haemophilus influenzae produce a
  slippery mucoid capsule that prevents phagocytosis by
  host immune cells
• Eliminate O-antigen on lipopolysaccharide (LPS) to
  diminish immune recognition and clearance.
• Biofilm bacteria are protected from antimicrobial agents,
  antibody and host immune cell, as shown in the Figure.

Question 25

Damage to the host tissue(s)

Answer 25

• Secreting enzymes that degrade host cell for nutrients
• replicating inside the cells and inducing apoptosis of the immune cell
• Toxins – substances that disrupt the normal metabolism of host cells
• Exotoxins
• Endotoxins
• Hypersensitivity reactions - inducing an excessive release of
  cytokines by immune cells and exacerbating inflammatory responses,
  destroying tissues

Question 26

Exotoxins

Answer 26

They are produced inside mostly gram + bacteria as part of their growth and metabolism
They are then released into the surrounding medium

Question 27

What are Endotoxins?

Answer 27

Part of the outer portion of the cell wall of gram - bacteria. They are liberated when the bacteria die and the cell wall breaks apart