W20 Microbe host interactions Flashcards
Define Symbiosis: !
What are the 3 symbiotic relationships?
=Close interaction between two organisms of different species
- Mutualism
- Commensalism
- Parasitism
What is Mutualism?
What is an example?
=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)
Define Commensalism:
What is commensal bacteria?
What is an example?
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
What is Parasitism? (relationship)
Example of a parasite?
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
Define Microbiota: !
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
Early Colonisation of Microbiota:
(for info)
- 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.
Dynamic and diverse microbiota composition: (!)
When does a human have a complete microbiota composition?
- 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
Name some Human microbiota body sites (!)
Which areas of the body are free of microorganisms?
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
Distribution and composition of normal
microbiota are determined by which factors? (4)
- Nutrients
- Physical and chemical factors
- Host defenses
- Mechanical factors
Name some Human microbiota functions: (!)
- Dietary fibre fermentation (resistant to host enzymes) into Short Chain Fatty Acids (source of energy)
- Synthesise and excrete vitamins (vit. K and B12)
- Prevent .colonisation by pathogens
-Competitive exclusion of pathogens
-Production or stimulation of antimicrobial molecules - Stimulate the development of certain tissues (intestines, lymphatic tissues, capillary density)
- Immune system stimulation/maturation
- Regulate inflammation
- Modulate and affect the central nervous system (Gut-Brain Axis)
What is Dysbiosis? (!)
What can it lead to?
What can it be caused by?
Examples?
=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
What can Fatty acids to do fatty acetyl coA?
Can convert into Fatty acetyl CoA and undergo Beta oxidation (4 steps) to produce Acetyl coA so it can enter the Krebs cycle
What are Opportunistic infections? (!)
- 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
What are Probiotics? (!)
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.
What are Prebiotics?!
Compound(s) added to enhance the colonisation and positive health benefits of probiotic microbes.
What are Synbiotics?!
Foods or supplements that include both a prebiotic and a probiotic.
Define an Opportunistic pathogen: (!)
May be part of normal microbiota and causes disease when the host is immunocompromised or when they have chance to outgrow
Define Pathogenicity:
Ability of a pathogen to cause disease
Define Virulence:
Degree of harm (pathogenicity) inflicted on its host.
What are the steps in pathogenesis of bacterial infections? (6)
- Entry of pathogens into the body*
- Attachment of the pathogen to some tissues
- Multiplication
- Invasion/spread of the pathogen
- Evasion if the host defences/immunity
- 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)
What occurs in Entry, adherence and colonisation? (!)
- Entry into the host
-Portal of entry
-Skin, respiratory, gastrointestinal, urogenital
systems, or conjunctiva of eye - Attachment of microbe to specific target cells (highly specific and permanent or nonspecific and reversible)
-Adherence structures:
-Pili
-Fimbriae
-Glycocalyx (Capsule) - Colonisation—establish a site of microbial replication on or within host
Define invasiveness
What are the 2 types?
= Ability to spread to adjacent tissues
- 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
Invasion - examples
- 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
Define: Overcoming Host Defences
Examples?
=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.
Damage to the host tissue(s)
- 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
Exotoxins
They are produced inside mostly gram + bacteria as part of their growth and metabolism
They are then released into the surrounding medium
What are Endotoxins?
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
