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Microbiology > Lecture 8: Bacterial Growth in the Lab > Flashcards

Lecture 8: Bacterial Growth in the Lab Flashcards

1
Q

Where can bacteria grow in a lab?

A
  • agar plates
  • broth
  • nutrient rich media
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2
Q

Growth in nutrient rich media takes on
the form of ________ growth

A

logarithmic growth

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3
Q

Logarithmic growth

A
  • Binary fission - 1, 2, 4, 8, 16…
     Growth rate can be expressed as doubling
    time
     E. coli has a doubling time in rich broth culture of 20 min
     More formally, N=N0e^kt
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4
Q

How to measure microbial growth?

A
  • perform measurements on liquid cultures only
  • plate counts
  • optical density (turbidity)
  • Microscopic visualization
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5
Q

Plate counts

A

count number of colony forming units (CFU) on plate

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6
Q

Optical density (turbidity)

A

direct measure the ability to absorb light at a specific wavelength

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7
Q

microscopic visualization

A

count bacteria in a given amount of culture directly

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8
Q

how to conduct plate counts?

A

 Dilute culture in an appropriate buffer/
medium (serial dilutions)
 If sample is very dilute, may use filtration method to concentrate instead
 Plate onto nutrient agar plates
 Count colonies (CFUs) after right amount of time (24h for standard
organisms)

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9
Q

Advantages and disadvantages of plate counts

A

advantage- only counts bacteria capable of dividing (CFU)
 Disadvantage- takes time to do; subject to experimenter error in dilution

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10
Q

How to do optical density (turbidity)

A

 Use a spectrophotometer
 Shines light at a specific
wavelength through the culture, measures the amount that passes
through (transmittance or its converse, absorbance)

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11
Q

Advantages and disadvantages of turbidity

A
  • Advantage- quick, accurate
    method for determining density of
    culture
     Disadvantage- may count dead cells
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12
Q

How to do microscopy?

A

 Take direct sample, count cells (use
hemocytometer or Petroff-Hauser cell counter)

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13
Q

Advantage and disadvantage of microscopy

A

 Advantage-quick, precise
 Disadvantage- may vary greatly from field to field, so need to observe many fields to get statistically relevant numbers
 Disadvantage- doesn’t distinguish live from dead cells
 Disadvantage- intensive compared to other two techniques
 This is not commonly used for cell counting

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14
Q

Logarithmic growth phases

A

bacterial culture growth has 4 phases
- lag
- log phase
- stationary phase
- death phase

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15
Q

Lag phase

A

when inoculating
a culture, cells take
time to adjust to new
environs

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16
Q

Log phase

A

maximal growth rate
 N=N0e^kt
 Calculate doubling time
(N=2N0)

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17
Q

Stationary phase

A

number of cells is
steady

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18
Q

Death phase

A

rate of cell death exceeds division rate

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19
Q

Solve N=Noe^kt
No=100, N =3200, t=300

A

3200 = 100e^k(300)
32 = e^300k
ln32 = 300k
ln32/300 = k
k = doubled

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20
Q

tD is when N = 2No

A

2No = Noe^ktD
2 = e^ktD
ln2 = ktD
tD = ln2/k

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21
Q

Solve N=Noe^kt
No=300, N =600, t= 60

then plug into tD equation

A

600= 300e^k(300-240)
2= e^k(60)
ln2 = 60k
ln2/60 = k

tD = ln2/(ln2/60)
tD = 60

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22
Q

What kind of culture does logarithmic growth curve describe?

A

batch cultures

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23
Q

What is batch culture?

A

The microbes are exposed to the same media, even as they utilize the nutrients and release various products

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24
Q

Where is continuous culture done?

A

in a chemostat

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25
What is continuous culture?
The spent media (containing bacteria) is removed, and fresh media added, at a constant flow rate
26
Chemostat culture graph
D = f/V - at low dilution rates, growth rate proportional to D (Monod) maintenance energy high dilution rates - washout
27
What environmental factors affect growth rate?
- temperature - pH - water activity - oxygen
28
psychrophilic
cold loving
29
thermophile
heat loving
30
mesophile
moderate temp. loving
31
hyperthermophile
high temp. loving
32
Why does temperature curves have that asymmetrical shape?
after you reach optimal temp. the cells immediately inhibit growth and eventually denature at the higher temperatures.
33
What do cardinal temperatures reflect?
reflect niche where normally found
34
What bacterium are found in skin (can tell by their cardinal temperatures 30-37)?
- listeria monocytogenes - staphylococcus aureus
35
acidophile
acidic condition loving
36
neutrophile
neutral pH loving
37
alkalophile
high pH loving
38
How does chemiosmosis work?
uses proton gradient to generate ATP across a membrane
39
compatible solutes
a molecule that doesn't interfere with the biochemistry happening in a cell, but pulls water into the cell ( or holds water in the cell) - modulate osmolyte concentration so it can quickly change whether to release or retain water.
40
how does bacteria make compatible solutes?
- manipulate ion flows across a membrane - make derivative compounds of simple ones they use a lot, to use them as a compatible solute temporarily (ex: trehalose)
41
osmotic pressure
solutes - salts
42
halophile
salty conditions
43
matric pressure
absorption to solids - desiccation
44
water activity
available water for organisms - proportion of water available for biochemistry
45
low water activity
makes life difficult
46
formula for water activity
aw = Psoln / Pwater
47
desiccation
loss of water? no water?
48
What protects against modest changes in water activity?
the cell wall
49
What happens at low water activity?
DNA disordering
50
What is botulism? What food is a known botulism carrier? Who is at risk of it?
Clostridium botulinum - a rare illness caused by a toxin that attacks the body's nerves and causes difficulty breathing, muscle paralysis, and even death - honey - babies, not adults because we already have bacteria in our gut so clostridium botulinum cant plant itself in our gut.
51
staphylococci
facultative anaerobes? (use oxygen when its there, doesn't use it when its not)
52
streptococci
aerotolerant anaerobe (ignore oxygen completely) - never aerobes - always anaerobes
53
Other factors on microbial growth
- radiation - pressure
54
Radiation
 UV, ionizing  DNA damage T-T dimers  Deinococcus radiodurans  Endospores
55
barophilic
high pressure
56
barotolerant
can survive high or normal pressures
57
piezophilic
- deep sea lives under elevated hydrostatic pressure
58
Liebig's law of the minimum
total biomass of organism determined by nutrient present at lowest concentration
59
Shelford’s law of tolerance
above or below certain environmental limits, a microorganism will not grow, regardless of the nutrient supply
60
Nutrient stress (oligotrophy) May result in ___________ in cells
physiological changes
61
Viable but non-culturable (VBNC)
 Can be identified by staining protocols  Postgate microviability  Morphological changes at single cell level  Many bacteria studied show capacity
62
All organisms need ____ and energy to survive
carbon
63
Carbon sources
- autotrophy - heterotrophy
64
autotrophy
fixation of carbon dioxide (gets it from the environment?)
65
heterotrophy
use of organic carbon
66
energy sources
- prototrophy - chemotrophy
67
phototrophy
energy from light
68
chemotrophy
energy from chemical reactions
69
photoautotroph
light and fix CO2
70
photoheterotroph
light and uses organic carbon
71
chemoautotroph
chemical rx and fix CO2
72
chemoheterotroph
chem rxs and uses organic carbon
73
Redox reactions generate...
cell energy
74
Where is the energy cells need stored?
in chemical bonds
75
what forms bonds in a molecule?
electrons
76
______ are moved between molecules by ____ reactions
- electrons - redox
77
In biological systems, oxidation of the nutrient is coupled with....
reduction of an electron carrier
78
What does a carrier do to electrons?
can transfer electrons from the nutrient molecule to other systems, where it is converted to ATP
79
OILRIG
- oxidation is loss - reduction is gain

Microbiology (16 decks)

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