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biology - component 1 > microbiology > Flashcards

microbiology Flashcards

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1
Q

define prokaryotae

A

the kingdom that bacteria are found in

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2
Q

define coccus

A

a spherical bacterium

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3
Q

define spirillum

A

spiral-shaped bacterium

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4
Q

define bacillus

A

rod-shaped bacterium

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5
Q

define gram positive

A

a bacterium which stains purple (due to crystal violet)

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6
Q

define gram negative

A

a bacterium which stains red (due to safranin)

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7
Q

define peptidoglycan

A

the only component of a gram positive bacterial cell wall

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8
Q

define lipopolysaccharide

A

layer of the cell wall found only in gram negative bacteria

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9
Q

define binary fission

A

process by which bacteria divide

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10
Q

define obligate aerobe

A

bacteria which can only survive and metabolise in the presence of oxygen

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11
Q

define obligate anaerobe

A

bacteria which can only survive and metabolise in the absence of oxygen

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12
Q

define facultative anaerobe

A

bacteria which prefer to metabolise in the presence of oxygen, but can metabolise in the absence of oxygen

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13
Q

define aseptic technique

A

process by which apparatus and equipment are kept free of microorganisms

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14
Q

define autoclave

A

sealed vessel in which glass and metal equipment are heated to 121C at high pressure to sterilise them

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15
Q

define total cell count

A

the total number of living and dead cells in a bacterial sample

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16
Q

define total viable count

A

total number of living cells in a known volume of liquid medium

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17
Q

define haemocytometer

A

microscope slide used to calculate the number of microbes in a sample

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18
Q

define serial dilution

A

a method of calculating viable count using repeated dilution of bacterial culture, assuming one colony will arise from one bacterial cell

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19
Q

under dilution causes what?

A

this causes colonies to merge (clumping) , making counting inaccurate

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20
Q

over dilution causes what?

A

this leads to there being too few colonies on each plate, making the results not statistically sound

21
Q

define turbidimetry

A

a method of indirectly counting cells using a colorimeter

22
Q

how can bacteria be distinguished by each other?

A
  • size
  • shape
  • staining characteristics
  • metabolic features
  • antigenic features
  • genetic features
23
Q

identify the structures in a bacteria

A
  • capsule
  • cell membrane
  • peptidoglycan cell wall
  • cytoplasm
  • plasmid
  • 70S ribosome
  • flagellum
  • circular DNA
24
Q

what is meant by autotrophic?

A

synthesize all their cell constituents using carbon dioxide as their carbon source

25
Q

what is meant by phototrophic?

A

photosynthesis with chlorophyll as e- donor

26
Q

outline how the gram staining technique works

A
  1. application of crystal violet
  2. application of grams iodine
  3. alcohol wash (decolourisation) - differential stage
  4. application of safranin
27
Q

what is the colour of gram positive bacteria after gram stain?

A

purple

28
Q

what is the colour of gram negative bacteria after gram stain?

A

red

29
Q

why do gram positive bacteria stain purple after gram stain?

A
  • have a thick peptidoglycan cell wall, but no outer lipopolysaccharide membrane
  • they therefore retain the initial crystal violet stain when washed with alcohol and appear purple under a microscope
30
Q

why do gram negative bacteria stain red after gram stain?
- what does this mean, in terms of susceptibility?

A
  • have a thin peptidoglycan cell wall and an outer lipopolysaccharide membrane.
  • when washed with alcohol they lose this layer with the crystal violet stain
  • instead they take up the counter stain safranin and appear red under a microscope
  • due to this difference, gram negative are not susceptible to some antibiotics such as penicillin, or lysosome
31
Q

what conditions are required for micro-organisms growth?

A
  • temperature
  • nutrients `
  • pH
  • oxygen requirements
32
Q

describe pH as a condition for bacterial growth

A

most bacteria favour slightly alkaline conditions, whereas most fungi grow better in neutral to slightly acidic conditions

33
Q

describe temperature as a condition for bacterial growth

A

as bacterial metabolism is regulated by enzymes, the range of 25-45C is suitable for most bacteria
- the optimum for mammalian pathogens is around 37C, the temperature of the human body

34
Q

describe nutrients as a condition for bacterial growth

A
  • in the laboratory nutrients are supplied in nutrient media, which may be provided as a nutrient agar or nutrient liquid broth
  • the carbon source is usually glucose
  • the nitrogen needed for amino acid and nucleic acid synthesis is provided as nitrate ions
35
Q

describe the population growth for microorganisms

A

4 stages:
1. lag - no/little cell division. intense metabolic activity such as enzyme synthesis
2. log - rapid increase in numbers, no limiting factors to growth. cell division > death rate. plenty of glucose available
3. stationary - limiting factors prevent further growth of the population e.g competition for glucose. carrying capacity has been reached
4. death - limiting factors cause the population size to decrease. death rate > cell division. this could be due to the build up of toxic waste, or no glucose left in the medium

36
Q

what are the 2 main purposes of aseptic techniques?

A
  1. preventing contamination of pure culture by microbes from the environment
  2. preventing contamination of the environment by cultures being grown
37
Q

outline the method of preventing contamination of pure culture by microbes from the environment

A
  • sterilise all media and equipment (such as inoculating loop) before use to prevent initial contamination
  • handle cultures carefully, flaming the neck of culture bottles before opening and closing
  • bunsen burner creating a convection current
  • disinfect work benches before hand - such as with 3% lysol
38
Q

outline the method of preventing contamination of the environment by cultures being grown

A
  • sterilise work surface before and after experiment using a disinfectant (lysol 3%)
  • lift lid of agar dish of 45 degrees
  • seal agar dish with adhesive tape in a cross shape
  • flame the neck of the culture bottle but do not place the cap down on the work surface
39
Q

outline the process of inoculating an agar dish
- which experiment is this used for?

A

used for GRAM STAIN
1. pass the metal inoculating loop through a flame until it is red hot. allow it to cool
2. hold the bottle containing the bacterial culture in one hand; remove the cap with the little finger of the other. do not place the cap down on the surface
3. flame the neck of the culture bottle for about 2-3 seconds. dip inoculating loop into bacterial culture
4. lift lid of the petri dish to 45 degrees to allow entry of inoculating loop and streak the agar with bacterial culture
5. secure the petri dish with adhesive tape ; do not seal all the way around the petri dish as this could lead to anaerobic conditions and potentially lead to the growth of pathogenic organisms
6. incubate at suitable temperatures 25-37C for 24-48 hours
7. sterilise all equipment after use

40
Q

how is glassware and metal equipment sterilised?

A

using an autoclave

41
Q

how is material in an autoclave sterilised?

A
  • sealed in an autoclave bag
  • heated to 121C in steam
  • under high pressure for 15 mins
42
Q

how is plastic (before use) sterilised?

A

e.g petri dish
sterilised by gamma radiation

once it has been used, it is disposed of in a biohazard waste bin or put in an autoclave

43
Q

in what two ways can the population of microorganisms in liquid culture be measured?

A

indirectly or directly counting cells

44
Q

define total cell count

A

living and dead cells in a bacterial sample

44
Q

define total viable count

A

living cells in a known volume of liquid medium

45
Q

what is the method for directly counting cells?

A

haemocytometer can be used to calculate the number of microbes in a sample
- haemocytometer is a microscope slide with a rectangular chamber at the centre which is engraved with a grid
- a coverslip is supported over the chamber and the depth of the chamber is known
- the number of cells in a specific volume of medium can be counted

46
Q

what does serial dilution assume?

A

a single bacterial cell will reproduce asexually to form a single colony of cells that can be seen (on an agar plate after incubation) and counted

47
Q

outline the method of serial dilution

A
  1. place 9cm3 of sterile distilled water into five sterile test tubes using a sterile pipette
  2. place 1cm3 of the original bacterial culture sample into the first test tube and gently mix. this has now been diluted 10 times
  3. transfer 1cm3 of this dilution from the first tube into the second tube containing water. it has now been diluted 100 times
  4. now transfer 1cm3 of each diluted sample onto a sterilise nutrient agar plate. use a sterilise spreader to spread the sample around
  5. repeat this twice more to give a total of 3 plates per dilution
  6. seal each agar plate with tape but not all the way around and incubate each agar plate at 25C for 24-48 hours
  7. after incubation, look for the dilution that shows distinct colonies without merging. count the number of distinct colonies
  8. multiply the number of colonies by the dilution factor to give the number of bacteria in the original 1cm3 bacterial culture sample
48
Q
A

biology - component 1 (6 decks)

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