Ch.4 Flashcards

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1
Q

Pure Culture

A
  • population of cells derived from a single cell
  • allows study of a single species
  • Organisms may behave differently than in nature
  • Only about 1% of microorganisms can be cultured
  • Pure culture obtained using aseptic technique: Minimizes accidental introduction of other organisms
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2
Q

Which technique is used to isolate bacteria from a mixed culture into a pure culture?

A

Streak-plate method
- Simplest, most commonly used method for isolating
- Reduces number of cells with each series of streaks
- Separated cells form distinct, isolated colonies

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3
Q

Which polysaccharide derived from Red Seaweed is used to solidify media for bacterial growth?

A
  • Agar used to solidify medium
    – Few microbes can degrade
    – Not destroyed by high temperatures and can be sterilized
    – Liquefies above 95 C
    – Solidifies below 45 C
    – Solid over temperature range for most microbial growth
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4
Q

Why is agar preferred over gelatin?

A

for its non-nutritive qualities, which allow for bacterial growth without being digested

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5
Q

In the growth curve of a bacterial population, at which phase are the bacteria rapidly increasing?

A

Exponential (log) phase:
- Cells divide at constant rate
– Generation time measured
– Most sensitive to antibiotics

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6
Q

During which phase of the bacterial growth curve does the total number of viable (live) cells decline?

A

Death phase:
- Total number of viable cells decreases at constant rate
- Exponential, but slower than cell growth

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7
Q

thermophile

A
  • 45 C to 70 C
  • love hot tempertures –> common in hot springs and compost heaps
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8
Q

What happens to proteins inside of bacteria that cannot survive these types of conditions?

A
  • Proteins of thermophiles resist denaturing
  • Thermostability comes from amino acid sequence
  • Number and position of bonds that determine structure
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9
Q

obligate aerobe

A

organism requires O2 to grow

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10
Q

Facultative aerobes

A

use O2, but don’t require it

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11
Q

Obligate anaerobes

A

cannot use O2

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12
Q

Aerotolerant anaerobes

A

obligate fermenters (can grow in O2, but they don’t use it)

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13
Q

How do high concentrations of salt and sugar in food help preserve food?

A
  • All microorganisms require water for growth
  • Dissolved salts, sugars make water unavailable to cell
  • Salt, sugar used to preserve food
  • If solute concentration is higher outside of cell, water diffuses out (osmosis)
  • Some microbes withstand or even require high salt
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14
Q

Which are the 6 major elements that are needed to build organic molecules and biological bodies?

A

Carbon
Hydrogen
Nitrogen
Oxygen
Phosphorus
Sulfur

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15
Q

What is the definition of “growth factors” when it comes to bacterial growth?

A

organic molecules that an organism cannot synthesize; must be present in the environment
- Growth factor requirements reflect biosynthetic capabilities
– Most E. coli strains synthesize all cellular components from glucose; no growth factors needed
– Neisseria species are fastidious; they require numerous growth factors, including vitamins and amino acids

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16
Q

What do the prefixes “Photo” and “Chemo” mean when it comes to microbial nutrition?

A

Photo = use light as an energy source
Chemo = gain energy from inorganic compounds

17
Q

Phototrophs

A
  • Phototrophs obtain energy from sunlight
    – Plants, algae, photosynthetic bacteria
18
Q

Chemotrophs

A
  • Chemotrophs extract energy from chemicals
    – Mammalian cells, fungi, many types of prokaryotes extract energy from organic molecules
19
Q

What do the prefixes “Hetero” and “Auto” mean when it comes to microbial nutrition?

A

Hetero = organisms incapable of making their own food from light or inorganic compounds
Auto = an organism that is self-nourishing or capable of generating its own food.

20
Q

Photoautotrophs

A

energy from sunlight; carbon from CO

21
Q

Photoheterotrophs

A

energy from sunlight; carbon from organic compounds

22
Q

Chemolithoautotrophs

A

energy from inorganic compounds; carbon from CO2

23
Q

Chemoorganoheterotrophs

A

energy and carbon from organic compounds

24
Q

What is the function of “selective” media?

A
  • Selective media inhibit growth of certain species in a mixed sample, while allowing growth of species of interest
    – Example: MacConkey agar is selective for Gram-negative rods
    – Contains crystal violet that inhibits Gram-positive bacteria and bile salts that inhibit most non-intestinal bacteria