Infection and Immunity - 1

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  • Created by: LBCW0502
  • Created on: 10-11-19 14:18
Describe features of symbiotic associations
Within life cycle, a micro-organism is in association with another organism. Relationships can change between infectious or healthy. Mutualism, commensalism, parasitism. Not static processes (move between nutritional states)
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What is commensalism?
Micro-organism associated with microbe of another species, doesn’t cause damage/no harm, associated with host (most common state), feeding but not at our expensive, microbe has shelter/protection to complete life cycle, live independently e.g. flora
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What is mutualism?
Association is essential for survival of both partners e.g. animals eating plant material containing micro-organisms, micro-organisms in gut (source of aromatic compounds/aromatic amino acids/aromatic vitamins, cannot synthesise this)
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What is parasitism? (1)
Nutritional association where micro-organism causes harm to its host e.g. during process of nutrition, reproduction, completing life cycle, seen as infection. Symptoms of parasitism (disease)
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What is parasitism? (2)
PParasite infecting human, may not initially cause infection (commensal), under certain conditions, can cause harm – disease. E.g. large numbers, overcome immune system, movement to different anatomical site, genetics, lack of immune cells
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What is parasitism? (3)
E.g. acne, micro-organisms in the colon move to the appendix (appendicitis), movement form gut to urinary tract.
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Give an example of how one person’s colonisation can become someone else’s infection (no harm to one person, cause infection to another)?
Meningitis amongst young people (university students). Despite vaccination, micro-organism might be colonised (transmission of micro-organisms)
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Describe features of the microflora of the skin (1)
Skin is the largest organ. Impenetrable barrier from environment, protection, hostile environment for micro-organisms (dry, lack of water, periods of drying, skin sheds/periodic shedding, microbes lost in the environment
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Describe features of the microflora of the skin (2)
Secretions/sweat/hyperosmotic/salt/lysozume breaks down peptidoglycan cell wall, cleaves linkage). pH of skin slightly alkaline. some microbes associated e.g. Staphylococcus epididymis (can have overgrowth e.g. acne)
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Describe features of the respiratory tract microflora (1)
Micro-organisms associated with the mouth but not many due to constantly swallowing – washing oral cavity with saliva (virulence factor – attachment to epithelium surface)
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Describe features of the respiratory tract microflora (2)
Nasal cavity – produce mucus to trap micro-organisms, cilia to waft mucus (virulence factor – attachment). Anaerobic environment. Most common disease (periodontal gum disease). Neisseria, Staphylococcus present
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Describe features of the respiratory tract microflora (3)
Trachea, lower respiratory tract – no normal population of microorganisms (only transient), defences to prevent microbes entering lower respiratory tract, cells for defence, coating of mucus to move microbes out of the lungs
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Describe features of the respiratory tract microflora (4)
(CF - can't clear mucus, infection develops, Pseudomonas)
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Describe features of the microflora of the GI tract (1)
No microflora of the stomach due to low pH (can have infection causing properties e.g. H.pylori). Stomach is relatively sterile/organisms transient. Few microbes in jejunum/ileum. Colon - large SA, microbes can colonise, large population of species
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Describe features of the microflora of the GI tract (2)
Association with large bowel, commensal organisms (beneficial for synthesis of aromatic compounds)
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Describe features of the microflora of the GI tract (3)
Process to control number of organisms – defecation, pass in one bowel motion 10^12/g weight of faeces, pass more microorganisms compared to indigestible material (importance of hand hygiene)
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Describe features of the microflora of the GU tract (female)
Micro-organisms from bowel can pass to other orifices (urethra, vagina), virulence factor (defy gravity, move upwards). Urinary tract actually sterile except at the urethra opening. Continuous washing – always producing urine (sterile areas)
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Which micro-organism is the main cause of female UTIs? (1)
E.coli. Organisms becoming resistant to antibiotics e.g. E.coli (causing UTI) – leading problem in the UK (AMR associated with urino-pathogenic E.coli strains, can be fatal in elderly patients
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Which micro-organism is the main cause of female UTIs? (2)
Commensal organisms, movement to different anatomical si
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Describe features of the microbiome in the vagina (1)
Under healthy conditions, pH of vagina is low ~ 4, not many microbes can survive, some do survive e.g. lacto-bacilli (feed off reduced carbon source- glycogen). Glycogen produced by vaginal epithelia (lining shed – release of glycogen)
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Describe features of the microbiome in the vagina (2)
Production of lactic acid (reduce pH) – similar to glycolysis process. pH controls numbers of other organisms.
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Describe features of the microbiome in the vagina (3)
Glycogen can stop being produced by vaginal epithelia (after menopause) no food source of lacti-bacilli, composition of microbiome changes (other organisms feed off other C sources and numbers increase) e.g. BV
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Describe features of the microbiome in the vagina (4)
Even if pH remains low, women can be exposed to other infections e.g. thrush (caused by yeast)
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What are virulence factors?
Factors responsible for infection/disease (e.g. genes, proteins)
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What are Koch's Postulates?
Organism must be found in all host's with disease. Organism must be isolated in pure culture. Organism should produce the same disease when inoculated into a healthy host. Organism should be re-isolated in pure culture
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What are the issues with Koch's Postulates? (1)
Not ethical to inoculate healthy host (e.g. needle-stick injury – inoculate healthy person with HIV, Ebola disease in Africa, healthy healthcare workers infected/die). Relies on organisms to be grown (can't grow all micro-organisms)
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What are the issues with Koch's Postulates? (2)
Able to prove Koch's postulate but cannot grow micro-organisms
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What is the molecular version of Koch's Postulates? (1)
Genes (or their products) have pathogenic potential (e.g. UC, CD, whimple disease). Gene should be found in all pathogenic strains but not in avirulent strains. Disruption of gene should reduce virulence
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What is the molecular version of Koch's Postulates? (2)
Avirulent strains can be transformed into virulent strains by cloning the gene (gene knockout). Gene must be expressed during infectious process. Gene product should elicit immune response (depends on host)
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Describe features of the transmissibility of the pathogen (1)
Transmission of pathogen from one human to another. E.g. direct contact/airborne, indirect airborne (pathogens survive in environment for long time), dust borne, organism on skin (skin sheds into environment), STIs (direct contact)
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Describe features of the transmissibility of the pathogen (2)
Transmission via vector e.g. insect, blood borne infection, insect bite, malaria, yellow fever (one mosquito, three different diseases/infections), formite objects (inanimate objects) microbes on surface (growing on food, raw food/commensal microbe
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Describe features of the transmissibility of the pathogen (3)
Animals’ colonisation could be a human infection
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Why is food kept at around 4 degrees Celsius? (1)
Metabolism of microbes is reduced, growth of organisms is reduced, number of organisms on surface of food is low, organisms still grow at low temperatures but slowly
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Why is food kept at around 4 degrees Celsius? (2)
(expiry date on food, cannot guarantee bioburden of food, may cause infection when eaten, also have expiry dates on medicines, non-sterile preparations)
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Describe features of adhesion and colonisation of the host (1)
Adhere to host, need to colonise on host (due to being prone to washing) e.g. uropathogen E.coli strains, not washed out with urine due to adhesion
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Describe features of adhesion and colonisation of the host (2)
Fibriae – long protein filaments to attach to epithelial surface, transient/break easily, adhesion molecule, bind to receptor on epithelial surface, allows organism to attach to epithelia
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Describe features of adhesion and colonisation of the host (3)
Organism can also produce a mucus layer itself – allow attachment to surface (biofilm forms, organism can multiply within biofilm, not washed away, more mucus produced, allows organism to move to different anatomical sites
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Describe features of adhesion and colonisation of the host (4)
Reason for organisms defying gravity, move up ureter, UTI, cannot clear biofilm). Difficult for antibiotics to reach effective concentration in biofilm (needs to diffuse into biofilm)
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Describe features of adhesion and colonisation of the host (5)
Organisms produce enzymes to break down mucus, movement across epithelial layer (e.g. skin, topical infection).
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Describe features of the invasion of the pathogen
After adhesion, colonisation, pass through epithelium surface, needs to survive in host, needs to become intracellular (invasion of pathogen). Taken up by cells which are not normally phagocytic, (C. albicans, causes thrush) e.g. all good bacteria
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Describe features of growth and multiplication (1)
Free iron is limiting in natural environments. Siderophores (catechols/hydroxamates) chelate free iron. Exotoxins can release bound iron from cells (virulence factors - production of toxins)
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Describe features of growth and multiplication (2)
Fe – cofactor of enzymes, but limiting in natural sources (bound to Hb, not free in circulatory system). Produce exotoxins to release bound iron from cells
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Describe features of the evasion of the immune response
Factor for success of microbe (pathogen) – evasion of host immune response (mechanisms - classical/adaptive and alternative/innate pathways, anti-phagocytic strategies). (see self-direct learning/revision points)
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Other cards in this set

Card 2

Front

What is commensalism?

Back

Micro-organism associated with microbe of another species, doesn’t cause damage/no harm, associated with host (most common state), feeding but not at our expensive, microbe has shelter/protection to complete life cycle, live independently e.g. flora

Card 3

Front

What is mutualism?

Back

Preview of the front of card 3

Card 4

Front

What is parasitism? (1)

Back

Preview of the front of card 4

Card 5

Front

What is parasitism? (2)

Back

Preview of the front of card 5
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