Microbe-host interactions: Microbiota and pathogens Flashcards
What are symbolic relationships?
when there are close interaction between two organisms of different species
Name the 3 types of symbiotic reletionships:
1) Mutualism
2) Commensalism
3) Parasitism
1) Bacteria – Host interactions: Mutualism
Both species (bacteria and host) benefit from their interactions
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)
2) Bacteria – Host interactions: Commensalism
One partner in the relationship benefits. The other neither benefits nor is harmed.
Benefit to the bacteria > Acquire nutrients consuming dead skin and a place to live and grow
Commensal bacteria may become pathogenic = disease
3) Bacteria – Host interactions: Parasitism
One partner, the pathogen, harms the host, causing infectious disease
Benefit to the virus > Virus takes advantage of the translational machinery of the cell to replicate (multiply) virus particles. Viruses = obligate intracellular parasites
Harm for the human cells > Viral infections = death of the cells and tissue damage
example of Mutualism:
Many hundreds of bacterial species living in the gut (gut microbiota/flora)
The human gut harbours trillions of microbes in healthy conditions
example of Commensalism:
Commensal bacteria colonise epithelial surfaces of skin 1 million bacteria on each square centimeter (cm2)
example of Parasitism:
SARS-CoV-2 infects human cells of the respiratory system, causing COVID-19
What is Microbiota
all the microorganisms that live in and on an organism
Approximately 1011 organisms
1-3% total body mass
Generally non-pathogenic
Symbiotic with host
EARLY colonization:
- Microbiota begins developing at birth
- Vaginal birth = exposure to microbes from the mother’s birth canal, whereas caesarean delivery = microbe exposure from initial caretakers
Bifidobacteria are important coloniser of the gut.
Ferment what?
sugars found in human breast milk provides the infant with calories and lowers the gut pH, limiting growth of pathogens
Dynamic and diverse microbiota composition
Microbiota is not static
It reach a adult-like composition by age 3
microbiota composition in adults
stable - without any major physical or lifestyle changes
vary from person
not only bac = some archaea, fungi, viruses present
Human microbiota body sites
determined by many factors:
Nutrients
Physical and chemical factors
Host defenses
Mechanical factors
do Internal organs and tissues (that is, brain, blood, cerebrospinal fluid, muscles) contain microorganisms
not normally
Distribution of microbiota niches (skin and mucous membranes) in the human body
- eyes
-mouth - nose and throat
- lungs
- skin
- stomach
- large intestine
- small intestine
- urogenital tract
What are the 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)
Dysbiosis
refers to an imbalance of microbial species and a reduction in microbial diversity within certain bodily microbiomes
what causes dysbiosis and what can it lead to?
- dietary changes
- antibiotic use
- psychological and physical stress
> > inflammation
Opportunistic infections
infection caused by commensals (part of the normal microbiota) that do not cause generally disease in a healthy host
Dysbiosis – altered microbiota
what can pathogen do?
outgrow
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.
Prebiotics
compound(s) added to enhance the colonization and positive health benefits of probiotic microbes.
Synbiotics
foods or supplements that include both a prebiotic and a probiotic.
Pathogen
Any organism that causes disease
Opportunistic pathogen
may be part of normal microbiota and causes disease when the host is immunocompromised or when they have chance to outgrowth
Pathogenicity
Ability of a pathogen to cause disease
Virulence
Degree of harm (pathogenicity) inflicted on its host
What are the 6 steps of Steps in pathogenesis of bacterial infections?
- 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) - 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)
3 steps; Entry, adherence and colonisation:
- Entry into the host
Portal of entry
Skin, respiratory, gastrointestinal, urogenital systems, or conjunctiva of eye - Attachment of microbe to target cell is first (high degree of specificity)
Adherence structures:
Pili
Fimbriae
Glycocalyx (Capsule) - Colonisation—establish a site of microbial replication on or within host
- Invasion (entry, adherence and colonisation)
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
examples of invasion
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
Overcoming Host Defences
step 5
Successful pathogens overcome competition and elude initial host responses as well as the adaptive immune system:
- overcoming host defences
bullet points
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
Overcoming Host Defences - examples
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 cells, inducing apoptosis of the immune cell
Toxins – substances that disrupt the normal metabolism of host cells
- Exotoxins
- Endotoxins
Hypersensitivity reactions - excessive release = cytokines by immune cells and exacerbating inflammatory responses, destroying tissues
Types of toxins
Exotoxins
Endotoxins
Exotoxins
produced inside mostly gram +ive bacteria as part of their growth and metabolism
released into surrounding medium
Endotoxins
part of outer portion of cell wall (lipid) of gram -ive bacteria
liberated when bacteria die and cell wall breaks apart
antimicrobial chemotherapy
administration of specific drug to treat infectious disease, having selective toxicity against pathogens involved in infections, not host cells
selectivity
take advantage of the difference between structure of the bacterial cell and the host’s cell
recap - fatty acids broken down
Fatty acid oxidation is the mitochondrial aerobic process of breaking down a fatty acid into acetyl-CoA units.
Fatty acids move in this pathway as CoA derivatives utilizing NAD and FAD.
Fatty acids are activated before oxidation, utilizing ATP in the presence of CoA-SH and acyl-CoA synthetase
