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IIH > Growth and identification of bacterial pathogens > Flashcards

Growth and identification of bacterial pathogens Flashcards

1
Q

Bacterial cells

Bacteria are 10x smaller than eukaryotic cells, what does this allow for

A

-rapid metabolism
-diffusion of nutrients is not limiting like in eukaroytes
– they can do rapid turnover of sugars, amino acids, and nucleotides
- which can help them build DNA n RNA

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2
Q

Bacterial growth

Why is bacterial growth under optimal conditions not a good thing?

A

They grow rapidly
but as a consequence this can cause sepsis (if your not quick with your antibiotics)

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3
Q

Media

What is microbiological media?

A

Liquid culture

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4
Q

Media

What do we use Microbiological media for?

A
  • Used to quantify growth rate (to see how quick they grow)
  • Study physiology of bacteria
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5
Q

Media

What is solid media?

A

Basically uses agar

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6
Q

Media

What is the use of solid media

A
  • Preliminary identification
  • Can work out the number of live bacteria
  • Can isolate a pure culture (1 colony)
    • so that there is no contaminants
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7
Q

Media

What is the use of selective media

A
  • Isolate specific bacteria,
  • inhibits growth of other bacteria
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8
Q

Media

What is the use of differential media

A
  • Ability to distinguish between different bacteria
  • see a difference between each other
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9
Q

Media

What is the use of macconkey agar

A
  • this is both selective and differential
    • inhibits the growth of bile salts and crystal violets
    • because bacteria don’t like growing in situations like this
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10
Q

Media

For macconkey agar we can use a pH indicator, what do the different colours represent?

A

below pH 6.8 = pink
neutral pH = colourless

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11
Q

Media

If we used macconkey agar to look at ecoli and salmonella?

What happens?

A
  • Ecoli forms pink columns
  • ferments lactose so pH drops so it changes colour
  • Salmonella does not ferment lactose (so it stays neutral)
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12
Q

Media

What do growth mediums need to contain?

A

-Carbon: In the form of glucose or other sugars
-Nitrogen: Anorganic (ammnonia, nitrate), or organic (like amino acids)
-Sulphur: (essential for amino acids)
-phosphorous: (required for ATP, DNA, RNA taken up as a inorganic phosphate)
-Minerals (Fe2+,Mg2+,Ca2+) -> needed for enzyme function

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13
Q

Media

What is a defined medium?

A
  • pure chemicals → means its very reproducible
  • used for ecoli
  • we know exactly what in this medium
  • it’s like a recipe, we know if you put in these exact amounts ecoli is going to grow
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14
Q

Media

What is complex media made from

A
  • Digests of microbial, plant and/or animal products
  • like marmite, or chicken stock
  • dehydrated infusion or porcine brains and hearts
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15
Q

Media

What does complex media support the growth of?

just think simply

A

lots of different bacteria

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16
Q

Microbial growth

What factors determine microbial growth?

just list them for now

A

-pH
-oxygen

17
Q

Microbial growth

How does pH determine microbial growth?

What is optimum growth pH

A
  • Grow optimally at neutral pH ( 7.4)
18
Q

Microbial Growth

What are the expceptiosn to bacteria that like growing at lower pH

Give an example and how it does it

A

h pylori
- causes stomach ulcers and grows at pH 3

-How does it do this?
-creates a micro-enviorment around the stomach, which has a more neutral pH
- it does this by producing ammonia and bicarbonate

19
Q

Microbial growth

The second factor that affects growth is oxygen?

How does o2 do this?

A

-aerobic bacteria breathe using mircobial respiration
- which is the best way to make ATP energy

20
Q

Microbial growth

Some bacteria don’t need oxygen, what are these bacteria called?

Type of bacteria

A
  • Aerotolerant anaerobes: can tolerate and grow in air
  • Obligate anaerobes: oxygen inhibits the growth of these guys or kills them
    • in the gut, a vast majority are obligate anaerobes

Anaerobes: don’t need respire oxygen

21
Q

Microbial growth

How do obligate anaerobes in the gut survive when they get excreted out?

A
  • they create spores
  • these can tolerate high heat, oxygen, UV
  • this structure protects DNA in the cell
  • when they are in environments that can facilitate their growth, they germinate
22
Q

Microbial growth

How do bacteria grow?

What are the 4 phases

A

-Lag
-Exponerial
-staionary
-death

23
Q

Microbial growth

What happens in the lag phase?

A
  • Need to adapt to new environments
  • need to start metabolising
    • generate ATP, ribosomes
24
Q

Microbial growth

What happens during the exponential phase?

A
  • divide every 20, to 30 minutes
  • rapid cell growth and metabolism
  • cells run out of one or more nutrients,
  • due to waste products limiting growth since there’s so many of them
  • these waste products can then accumilate
25
Q

Micorbial growth

What happens in the stainoary phase

Expand on the points as well

A
  • no more growth
  • slow growth
  • start preparing for survival (so can make spores)
  • they are resistant to stress because they switch on all sorts of defence mechanisms
    • harder to treat, maybe more resistance to antibiotics
  • they also produce antibiotics to kill their neighbouring cells
  • if you kill the neighbouring cells, then you can take their nutrients, and recycle them, to grow you’re self

If you did not get the explanations rate this 2

26
Q

Microbial growth

What happens in the death phase?

A

they die because they have no nutrients to grow

27
Q

Identifying bacteria

How do we identiy bacteria using the gram stain

A
  • You first use crystal violet,
  • and then wash it out with ethanol,
  • and then positive bacteria will retain the crystal violet so we can see them
  • with gram negative since we cant see them
  • so we stain them using safranin
28
Q

identifying bacteria

The gram stain allows us to visualise bacteria, How do we classify these bacteria?

A
  • Gram negative bacteria (light pink)
  • Gram-positive bacteria (dark purple)
29
Q

Identifying bacteria

What’s the difference between gram negative and gram positive bacteria

A

Gram-positive bacteria

  • have a single cell wall
  • but have a larger layer of peptidoglycans

Gram-negative bacteria

  • have two membranes
  • but a thin layer of peptidoglycans
30
Q

Why is it important to use gram stains

like how does it help us and what are the implications of some bacteria

A
  • use it to premlimnary identify bacteria

Why?
- important because differences in cell wall, has impact on what antibiotics we can use

31
Q

Identifying bacteria

Gram negative bacteria are more resistant to antiboitics than gram poistive.

Why?

A

Gram negative bacteria only few antibiotic, can target that second cell wall

32
Q

Clinical microbiology

A
33
Q

What is direct microscopy and what are the advantages

A

standard light microscope
staining

Advantages
cheap
fast
useful in low-resource settings

IIH (7 decks)

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