Microbiology > Chapter 4 > Flashcards

Chapter 4 Flashcards

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1
Q

Bacteria Growth

A
  • Refers to increase in bacterial cell numbers - not an increase in size of individual cells
  • Most bacteria reproduce by binary fission
  • The bacterial cell:
    1) Elongates and makes a copy of its DNA
    2) Divides into two identical cells
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2
Q

Exponential Growth

A
  • Because bacteria divide by binary fission, the population of cells will double every generation
  • Time required for population to double = generation time
  • Varies greatly between different bacteria
  • E.coli has generation time = 20 minutes
  • Mycobacterium tuberculosis = 24 hours
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3
Q

Bacterial Growth in the Lab

A
  • Culture: microbes growing in a medium

- Inoculation: introducing microbes into a medium to start a culture

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4
Q

Batch Culture

A
  • Closed system
  • One started, no other nutrients added
  • When nutrients are used up - bacteria stop growing
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5
Q

Continuous Culture

A
  • Open system

- Nutrients are continuously added, wastes are continuously removed - supports indefinite growth

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6
Q

The Growth Curve in Batch Culture

A

1) Lag Phase
2) Exponential Phase (Log Phase)
3) Stationary Phase
4) Death Phase
5) Phase of Prolonged Decline

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7
Q

Lag Phase

A
  • Period of adaptation

- Cells adjust to new media and get ready to grow

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8
Q

Exponential Phase

A
  • Period of maximal reproduction - Cell numbers increase exponentially
  • Used to calculate generation time
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9
Q

Stationary Phase

A
  • Cells have reached maximum population density
  • Nutrients have been used up, or wastes have accumulated
  • No increase in cell number
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10
Q

Death Phase

A
  • Toxic waste products have accumulated

- Cells die at a uniform rate

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11
Q

Phase of Prolonged Decline

A
  • Sometimes a small fraction of population survives the death phase
  • May consume nutrients released from dying cells
  • Selects for the strongest cells in the population
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12
Q

Temperature Requirements

A
  • Each species of microbe has its own specific temperatures range
  • This range usually spans about 30 degree C
  • Minimum = lowest temp supporting growth
  • Optimum = temperature that supports best growth
  • Maximum = highest temp supporting growth
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13
Q

Psychrophiles

A
  • Cold loving
  • Grow between 5 to 15 degree C
  • Killed at 20
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14
Q

Psychrotrophs

A
  • Have a very broad temp range
  • Min: about 5
  • Max: About 30-45
  • Optimum: 15-30
  • These are the microbes that cause food to spoil in your fridge
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15
Q

Mesophiles

A
  • Moderate temperature loving
  • Min: about 10
  • Max: about 45
  • Optimum: 25-45
  • Most bacteria are mesophiles
  • Most pathogens (diseases causing microbes) have temperature optimum of 37 degree C
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16
Q

Thermophiles

A
  • Heat loving
  • Min: about 40
  • Max: about 80
  • Optimum: about 65
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17
Q

Hyperthermophiles

A
  • Min: about 75
  • Max: up to 121
  • Restricted to very few places on earth where water reaches these temperature (deep ocean vents)
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18
Q

Food Safety

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A
  • Involves the use of both hot and cold temperatures
  • Heat is used to kill mesophilic and psychotropic microbes (Cooking)
  • Cold temp is used to slow growth – Only psychrotrops will grow in a refrigerator and slowly
19
Q

Obligate Aerobes

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A

Require O2 for respiration (energy generation)

20
Q

Facultative Anaerobes

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A

Can use O2 for respiration but can also grow in its absence

21
Q

Obligate Anaerobes

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A

Cannot use O2 and are killed by it

22
Q

Microaerophiles

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A

Require O2 in low amounts, but killed by high concentrations

23
Q

Aerotolerant Anaerobes

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A

Cannot use O2, but are not killed by it

24
Q

pH

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A
  • Measurement of acidity or alkalinity
  • pH below 7 = acidic
  • pH above 7 = alkaline
  • pH of 7 = neutral
  • Most bacteria grow at or near neutral pH (6.5-7.5)
  • Bacteria that grow at very low pH: Acidophiles
  • Bacteria that grow at high pH: Alkaliphiles
25
Osmotic Pressure
- Osmosis is the movement of solvent molecules across a semi-permeable barrier - Ex. Movement of water through the cytoplasmic membrane - H2O will move from area of high concentration to area of low concentration - Osmotic pressure is important in food preservation - Some bacteria have adapted to life in high salt concentrations - requiring up to 30% NaCl = extreme halophiles - bacteria that live in the Dead Sea - Blood has a salt concentration of about 0.9% (does not inhibit growth of microorganisms)
26
Hypertonic Solution
- High solute concentration - Ex. Salt or Sugar - Water flows out of the cell - Cell dries up - plasmolysis
27
Hypotonic Solution
- Low solute concentration - Water flows into cell - Cell bursts - Osmotic Lysis
28
Isotonic Solution
Condition where solute concentration on outside of cell is equal to that inside the cell
29
Carbon (Nutritional Factors that Influence Growth)
- Required for all organic molecules - backbone of living matter - Heterotrophs - Take carbon from organic matter - sugars - Autotrophs - Use inorganic carbon - CO2
30
Nitrogen, Sulfur, and Phosphorus (Nutritional Factors that Influence Growth)
- Required in smaller amounts for synthesis of cellular material - Example: Protein, Nucleic Acids, Phospholipids, ATP
31
Trace Elements (Nutritional Factors that Influence Growth)
- Required in very small amounts | - Example: Iron, Zinc, Molybdenum
32
Energy (Nutritional Factors that Influence Growth)
- Organisms need energy to build cell material and drive cellular processes - Phototrophs - Harvest energy from sunlight - Chemotrophs - acquire energy from chemical compounds - May be organic or inorganic (Sugars)
33
Nutritional Diversity
Organisms are classified based on how they obtain their carbon and energy - Photoautotrophs - Photoheterotrophs - Chemoautotrophs - Chemeoheterotrophs
34
Photoautotrophs
- Use sunlight for energy - CO2 as carbon source = Photosynthesis - Includes - some bacteria (Algae and Plants)
35
Photoheterotrophs
- Use sunlight for energy | - Obtain organic carbon from food - some bacteria
36
Chemoautotrophs
- Obtain energy from inorganic chemicals - Use CO2 as carbon source - Only done by some bacteria
37
Chemeoheterotrophs
- Obtain energy from organic chemicals - Use the same organic chemicals as their source of carbon - All animals, fungi and protozoa - Most bacteria - All medically relevant bacteria are chemoheterotrophs
38
Solid Media (Agar Petri Plates) (Culture Media)
- Made by adding agar (solidifying agent) to liquid media - cannot be degraded by most bacteria - Allows growth of colonies: 1) A genetically identical population of cells 2) Allow the isolation of pure cultures
39
Chemically Defined (Culture Media)
- The exact chemical composition of the medium is known - Ex. Media made from known quantities of salts and sugars - Also known as minimal media
40
Chemically Undefined (Culture Media)
- Contains rich organic ingredients (so the chemical composition is not known) - Ex. Media containing yeast extratct (all of the soluble components from crushed yeast cells) - Also known as complex media
41
Selective Media
- Prevents the growth of unwanted organisms, allowing only the desired microbes to grow - Ex. Bismuth sulfite agar - used to culture Salmonella typhi - Inhibits growth of all Gram positive and most Gram negative bacteria
42
Differential Media
- Used to distinguish different bacteria - All can grow - but colonies of certain bacteria look different the plate - Ex. Blood agar plates - Used to distinguish bacteria that can lyse (and eat) red blood cells (Streptococcus pyogenes)
43
Direct Count
- Cells are counted using a light microscope - Usually employs a special counting chamber - Inaccurate because it counts both live and dead cells
44
Visible Counts
- Only live cells are counted - A liquid culture is diluted and plated onto agar plates to grow colonies - Each colony on a plate represents a single cell from the original culture - Colonies are counted, and used to calculate the number of bacteria in the original culture - Counts are always expressed as cfg per ml: colony forming units - assumption is that 1 cfg = 1 live bacterial cell
Microbiology
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