Microbiology Flashcards

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1
Q

Draw and label the structure of a prokaryotic cell

A
Flagellum
Pilus
Circular DNA
Plasma Membrane
70s Ribosome
Peptidoglycan Cell Wall
Slime Capsule
Plasmid
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2
Q

What is the function of the plasma membrane in a prokaryote?

A
  • barrier between the environment and the cytoplasm

- controls entry and exit of substances into and out of the cell

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3
Q

What is the function of the peptidoglycan cell wall in a prokaryote?

A
  • prevents osmotic lysis

- rigidity and cell structure

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4
Q

What is the function of the slime capsule in a prokaryote?

A
  • protect against other cell attack

- prevents cell drying out

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5
Q

What is the function of pili in a prokaryote?

A

Transferring plasmids (genetic information) by conjugation

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6
Q

What is the function of the flagellum in a prokaryote?

A

For mobility

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7
Q

What is the function of the plasmid in a prokaryote?

A
  • contains extra bacterial genes, e.g. bacterial resistance

- can be exchanged between bacteria during conjugation allowing spread of resistance

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8
Q

What are the 3 bacterial shapes?

A
  1. Bacillus (Rod)
  2. Coccus (sphere)
  3. Spirillum (Spiral)
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9
Q

What are prokaryotes?

A
  • no membrane bound nucleus
  • no membrane bound organelles
  • small ribosomes (70s)
  • cell wall made up of peptidoglycan
  • small cells, 0.5-5um
  • reproduce by binary fission
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10
Q

What is the structure of gram positive bacteria?

A
  • cell wall has a thick layer of peptidoglycan and a plasma membrane
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11
Q

What happens to gram positive bacterium in the Gram stain?

A
  • peptidoglycan holds onto crystal violet dye

- dye is not washed out by ethanol and therefore appears purple in the Gram stain

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12
Q

What is the structure of Gram negative bacterium?

A
  • thick outer layer of lipopolysaccharides with a thin layer of peptidoglycan
  • plasma membrane beneath
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13
Q

What happens to Gram negative bacterium in the Gram stain?

A
  • crystal violet dye is removed when rinsed with ethanol (dissolves the stained lipopolysaccharide layer)
  • peptidoglycan is stained with the counter-stain and therefore appears pink in the gram stain test
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14
Q

What antibiotics interfere with Gram positive bacterium?

A
  • Penicillin
  • prevents bonds interlinking peptidoglycan forming
  • when the bacteria divide, the cell walls are weak and collapse
  • water uptake by osmosis bursts the cell
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15
Q

What antibiotics interfere with Gram negative bacterium?

A
  • Require antibiotics that interfere with the cell’s metabolism/protein synthesis
  • e.g. vancomycin
  • penicillin is not effective as the outer layer protects the peptidoglycan
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16
Q

Why are animal cells not damaged by penicillin?

A

Animal cells do not have a cell wall, not damaged by penicillin

17
Q

Definition of a Gram Stain

A

A method of staining the cell walls of bacteria as an aid to their identification

18
Q

What is the method for the Gram-stain test?

A
  1. create a flame-fixed emulsion of bacterial samples on a slide
  2. flood with crystal violet, leave for 1 min then rinse of excess with sterile distilled water
  3. Add lugol’s iodine solution, leave for 1 min then rinse
  4. Flood with decolouriser (ethanol) for 30 seconds until run-off is clear
  5. Counter-stain with Safranin, leave for 1 min then rinse
  6. Gently blot dry slide
  7. Observe slide under oil immersion on a microscope
19
Q

Why do you add alcohol/ethanol?

A

Alcohol removes unbound stain and lipopolysaccharide layer

20
Q

Conditions necessary for growth and bacteria: temperature

A
  • 25-45’c as metabolism is regulated by enzymes.

- mamallian pathogens optimum is 37’c

21
Q

Conditions necessary for growth and bacteria: pH

A
  • pH 7.4
  • slightly alkaline conditions
  • fungi prefer neutral to acidic conditions
22
Q

Conditions necessary for growth and bacteria: oxygen

A
  • some require oxygen

- some require anaerobic conditions

23
Q

Conditions necessary for growth and bacteria: nutrients

A
  • need a carbon and energy source ususally glucose
  • need nitrogen source in organic or inorganic form for amino acid synthesis
  • need growth factors; minerals and vitamins
24
Q

What is the aseptic technique when handling bottles and caps?

A

Hold bottle cap in little finger and flame the bottle neck beofre and after extracting bacteria

25
Q

Why is sterilisation important?

A

To stop contamination of environment from culture and contamination of culture from environment

26
Q

Define obligate aerobes

A

require oxygen to survive

27
Q

Define obligate anaerobes

A

require anaerobic conditions to survive, oxygen is toxic

28
Q

Define facultative anaerobes

A

grow better in the presence of oxygen but can survive in it’s absence

29
Q

What is the method for serial dilution?

A
  • 9cm3 of sterile water is placed in a series of 6 sterile tubes
  • using a sterile pipette add 1cm3 of culture into first tube
  • transfer 1cm3 from the first tube into the second
  • repeat this for all six tubes
  • transfer 1 cm3 of eavh sample onto a sterile petri dish for each of the six tube onto agar plate
  • seal plates with tape and incubate at 25’c
30
Q

How to estimate population size from a serial population?

A
  • let the bacteria grow
  • select a dish containing 20-200 colonies that are distinct and sperate
  • count the number of colonies
  • multiply by the appropriate dilution factor
31
Q

What is turbidity?

A
  • indirect method
  • cloudiness of culture is measured as bacteria numbers increase
  • uses a colourimeter
  • then population is read off calibration culture
32
Q

Why is important in serial dilution to count between 20-200 colonies?

A
  • over 200 is too greater number to count and make sure there is no overlap
  • under 20 as there is a greater risk of accumulated error if two bacteria are in one colony
33
Q

Why is important in serial dilution to count between 20-200 colonies?

A
  • over 200 is too greater number to count and make sure there is no overlap
  • under 20 as there is a greater risk of accumulated error if two bacteria are in one colony
34
Q

What aseptic techniques are used?

A
  • steriles all equipment by autoclaving at 121’c for 15 minutes
35
Q

What can obligate anaerobes not do in the presence of oxygen?

A

Metabolise