Topic 6: Immunity Flashcards
What is immunity?
having sufficient B&T memory cells to avoid disease
What is natural active immunity?
being exposed to antigen of pathogen, leading to antibody production and memory cells being made
What is natural passive immunity?
antibodies received from mother to foetus but no memory cells are made
What is active artificial immunity?
exposure to antigen via vaccine leading to antibody production and memory cells being made
What is passive artificial immunity?
antibodies received by injection but no memory cells are made
What is in a vaccine? (5)
- live, attenuated pathogen
- dead pathogen
- antigen of pathogen
- related organism with similar antigen
- toxoids
Why are booster injections needed?
re-exposure to antigen to increase number of B and T memory cells to maintain protective levels
What is herd immunity?
when a high enough proportion of the population is vaccinated to also protect those without immunity
Why is there no HIV vaccine?
- difficulty in producing global vaccines
- virus mutates frequency; many subtypes
What are the pros of vaccination?
- herd immunity: wider population protected
- RO number kept low
- harmful outbreaks prevented
- burden on hospitals lessened
What are the cons of vaccination?
- no vaccine gives 100% protection
- risk of adverse reactions
How do bacteriostatic antibiotics work?
Prevent multiplication (no cell division) so that immune system can destroy pathogen. They do this by:
- targeting protein synthesis
- targeting DNA replication
- targeting RNA transcription
How do bactericidal antibiotics work?
Kill bacteria via cell lysis by:
- targeting bacteria cell wall
- targeting bacteria cell membrane
- interfering with enzyme activity
Why do antibiotics not affect human cells?
they only stop protein synthesis in 70s ribosomes; eukaryotes have 80s ribosomes
How is antibiotic efficacy tested?
Mastring:
- Use wire inoculation loop to transfer bacteria to agar plate
- Add standard amount of antibiotic onto paper discs, without control disc soaked in water
- Tape a lid onto petri dish and incubate at 37C for 24-48 hours
What does the clear zone tell you?
shows areas where bacteria can’t grow so the larger the clear zone, the better the antibiotic
List some aseptic techniques (3)
- Regularly disinfecting surfaces to minimise contamination
- Work near a Bunsen burner so any microbes in the air don’t reach the culture
- Sterilise wire inoculation loop after each use by passing through Bunsen burner flame
What is in nutrient agar? (5)
- Protein to provide nitrogen
- Yeast to provides vitamins, carbs, salt
- NaCl to reflect salt conc of cytoplasm
- Distilled water as transport medium
- Buffer to adjust pH to neutral
Why do we still have genetic diseases?
carriers of some genetic diseases have resistance against some microbial diseases (heterozygous advantage)
Why do bacterial populations evolve so fast?
- reproduce frequently
- high mutation rate
What are the selection pressures on bacteria?
- immune system
- antibiotics
How can pathogens evade the immune system?
- antigenic drift
- antigenic shift
What is antigenic shift?
changes in antigens due to mixing of antigens from different species
What is antigenic drift?
changes in antigens due to mutations
How does M. tuberculosis evade the immune system?
- resistant to digestion by enzymes in lysosome
- can survive inside macrophages
- destroy macrophages and infect others
How does HIV evade the immune system?
- antigenic shift and drift
- infects T helper cells, lies dormant and then kills them
How do pathogens beat antibiotics?
- pump out
- degrade
- alter
How do bacteria pass on resistance genes?
- horizontal gene transfer via plasmid containing resistance gene
- natural selection: resistant bacteria reproduce passing on genes
Which strategies can reduce the prevalence of HCAIs?
- More hand wash stations
- Thorough cleaning of wards
- Only using antibiotics when BACTERIAL infection
- Isolating infected patients
