Microbiota + Pathogens

Question 1

What is symbiosis?

Answer 1

close interaction
between two organisms of different
species

Question 2

What are the three different types of symbiotic relationships?

Answer 2

• Mutualism
• Commensalism
• Parasitism

Question 3

What is mutualism?

Answer 3

*both species benefit from the interactions

Question 4

What is an example of mutualism and how it benefits the bacteria and human/host?

Answer 4

• Bacterial species living in the gut (gut microbiota/flora)
  The human gut harbours trillions of microbes

Benefit to the bacteria → Nutrients availability, physical requirements for their growth
(anaerobic conditions, pH suitability)

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 5

What is commensalism?

Answer 5

*one partner in the relationship benefits
*the other neither benefits nor is harmed

Question 6

What is an example of commensalism and how it benefits bacteria?

Answer 6

Commensal bacteria colonise epithelial surfaces of skin
E.g. Streptococcus epidermis

Benefit to the bacteria → Acquire nutrients, ability to grow, colonising niches, without causing neither harm nor help

Commensal bacteria may become opportunistic pathogenic (e.g. via broken skin) and cause disease

Question 7

What is parasitism?

Answer 7

• One partner, the pathogen, harms the host, causing infectious disease

Question 8

What is an example of parasitism + how this benefits/harms?

Answer 8

• SARS-CoV-2 or Influenza viruses 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, tissue damage and inflammation.

Question 9

What is microbiota?

Answer 9

all the microorganisms that
live in and on an organism

Question 10

When does microbiota develop + where? + differences in birth

Answer 10

*microbiota begins developing at birth
*vaginal birth provides different microbiota than caesarean delivery
*breastfeeding affects microbiota
*bifidobacteria are important coloniser of the gut
- can ferment sugars found in human breast milk provides the infant with calories and lowers gut pH, limiting growth of pathogens.

Question 11

What is the composition of microbiota?

Answer 11

*microbiota, bacteria, archaea, fungi and viruses reach adult like composition by age 3
*relatively stable in adults, changes with physiological states or lifestyle (diet, stress antibiotic therapy)
*variable from person - person, reduced variability in the elderly

Question 12

What factors affect what/how microbiota are determined?

Answer 12

*nutrients
*physical and chemical factors
*host defences
*mechanical factors

-internal organs and tissues (brain, blood,cerebrospinal fluid, muscles) are normally free of microorganisms

Question 13

What are the two types of microbiota species?

Answer 13

*resident flora
*transient flora

Question 14

What is resident flora?

Answer 14

*permanently colonising host

Question 15

What is transient flora?

Answer 15

*temporarily present with limited presence

Question 16

What are the functions of human microbiota?

Answer 16

*protection against pathogens/infections
*regulate inflammation
*stimulate tissue development (intestines, lymphatic, capillary density)
*dietary fibre fermentation into short chain fatty acids
*synthesise vitamins (vit K and B12)
*modulate and affect the CNS (gut-brain axis)

Question 17

How do human microbiota protect against pathogens/ infections?

Answer 17

• Competing for nutrients
• Exclusion of binding sites, preventing pathogens attachment/colonisation
• Production or stimulation of antimicrobial molecules
• Immune system stimulation/maturation

Question 18

What is dysbiosis?

Answer 18

*imbalance of microbial composition
→ reduction in microbial diversity
can be caused by: diet, stress (psycho or physio) including oral Broad spectrum antibiotic use
↓
can cause diseases that involve inflammation.

Question 19

What is an opportunistic infection?

Answer 19

Infections caused by commensals (normal microbiota) that do not usually harm the
host in a healthy individuals but in some cases can become opportunistic pathogen

Question 20

What is an immunocompromised patient + when?

Answer 20

= permanent or temporary weakened immunity
*after treatments (anticancer chemo)
*after surgery
*disease (HIV)
*malnutrition - alcoholism - drug abuse - genetic defects

Question 21

What is a probiotic?

Answer 21

live microorganisms to restore the normal balance of microbiota (gut and genital tract) and related functions, conferring a health benefit.

Question 22

What is a prebiotic?

Answer 22

Non-digestable fibre compounds to stimulate the growth and colonisation of probiotic microbes within a microbiota → probiotic food

Question 23

What is a synbiotic?

Answer 23

supplements that combine both prebiotics and probiotics

Question 24

What is the definition of a pathogen?

Answer 24

any microorganism that causes disease in a defined host.

Question 25

What is the definition of a opportunistic pathogen?

Answer 25

component of normal microbiota that can cause disease when host is immunocompromised or when they have chance to outgrowth.

Question 26

What is the definition of pathogenicity?

Answer 26

ability of a pathogen to cause disease.

Question 27

What is virulence?

Answer 27

degree of harm (pathogenicity) inflicted on its host.

Question 28

What are the steps in pathogenesis of bacterial infections?

Answer 28

1. Entry of pathogens into the body Any organism that causes disease according to the transmission routes (e,g. penetration, inhalation, ingestion and introduction into the blood) 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)

Question 29

What is entailed in the attachment of microbe to specific target cells?

Answer 29

*pili *fimbriae *glycocalyx (capsule) all adherence structures

Question 30

What is invasiveness?

Answer 30

ability to spread to adjacent/deeper tissues.

Question 31

What are virulence factors?

Answer 31

adaptations used by microbes to invade and cause the host tissue damage

Question 32

What is entailed in invasion? (active and passive) step 4

Answer 32

Active - (high virulent pathogens breaching tissue barriers and disrupt the tissue integrity through secretion of: * Toxins - poisonous for host tissues * proteolytic enzymes – to dissolve tissue components *E.g. C. difficile toxins disrupting the intestinal lining Passive - exploiting pre-existing tissue alterations >skin lesions, insect bites and wounds

Question 33

What is entailed in overcoming host defences? (step 5)

Answer 33

* Find shelter to avoid recognition by immune cells (surviving and replicating inside or between host cells, within biofilms) * Avoid phagocytosis (capsule). * Produce enzymes that inactivate innate immunity. * Mutate and/or reduce cell surface proteins detected by immune cells

Question 34

What is entailed in damage to host tissues? (step 6)

Answer 34

* secreting proteolytic enzymes that degrade host cell for nutrients * replicating inside the host cells and inducing apoptosis * Toxins – disrupting the normal structure and function of host cells/tissues * Exotoxins * Endotoxins * Inducing hypersensitivity reactions - excessive release of cytokines by immune cells and exacerbating inflammatory responses, even life threating shock syndrome

Question 35

What is the overview of exotoxins?

Answer 35

*produced inside mostly +ve gram bacteria *released into surrounding medium

Question 36

What is the overview of endotoxins?

Answer 36

*part of outer section of cell wall of -ve gram bacteria *liberated when bacteria die and cell wall breaks apart