1. Microbiota begins developing at birth 2. Vaginal birth = exposure to microbes from the mother’s birth canal, whereas caesarean delivery = microbe exposure from initial caretakers

Microbe-host interactions: Microbiota and pathogens Flashcards by Casi Jones

What are symbolic relationships?

when there are close interaction between two organisms of different species

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Name the 3 types of symbiotic reletionships:

1) Mutualism
2) Commensalism
3) Parasitism

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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)

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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

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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

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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

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example of Commensalism:

Commensal bacteria colonise epithelial surfaces of skin 1 million bacteria on each square centimeter (cm2)

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example of Parasitism:

SARS-CoV-2 infects human cells of the respiratory system, causing COVID-19

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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

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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

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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

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Dynamic and diverse microbiota composition

Microbiota is not static

It reach a adult-like composition by age 3

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microbiota composition in adults

stable - without any major physical or lifestyle changes

vary from person

not only bac = some archaea, fungi, viruses present

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Human microbiota body sites
determined by many factors:

Nutrients
Physical and chemical factors
Host defenses
Mechanical factors

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do Internal organs and tissues (that is, brain, blood, cerebrospinal fluid, muscles) contain microorganisms

not normally

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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

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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)

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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?

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)

3 steps; Entry, adherence and colonisation:

1. Entry into the host Portal of entry Skin, respiratory, gastrointestinal, urogenital systems, or conjunctiva of eye 2. Attachment of microbe to target cell is first (high degree of specificity) Adherence structures: Pili Fimbriae Glycocalyx (Capsule) 3. Colonisation—establish a site of microbial replication on or within host

4. 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:

5. 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

6. 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