Chapter 4 Flashcards
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
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
3
Q
Bacterial Growth in the Lab
A
- Culture: microbes growing in a medium
- Inoculation: introducing microbes into a medium to start a culture
4
Q
Batch Culture
A
- Closed system
- One started, no other nutrients added
- When nutrients are used up - bacteria stop growing
5
Q
Continuous Culture
A
- Open system
- Nutrients are continuously added, wastes are continuously removed - supports indefinite growth
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
7
Q
Lag Phase
A
- Period of adaptation
- Cells adjust to new media and get ready to grow
8
Q
Exponential Phase
A
- Period of maximal reproduction - Cell numbers increase exponentially
- Used to calculate generation time
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
10
Q
Death Phase
A
- Toxic waste products have accumulated
- Cells die at a uniform rate
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
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
13
Q
Psychrophiles
A
- Cold loving
- Grow between 5 to 15 degree C
- Killed at 20
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
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
16
Q
Thermophiles
A
- Heat loving
- Min: about 40
- Max: about 80
- Optimum: about 65
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)
18
Q
Food Safety
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
A
Require O2 for respiration (energy generation)
20
Q
Facultative Anaerobes
A
Can use O2 for respiration but can also grow in its absence
21
Q
Obligate Anaerobes
A
Cannot use O2 and are killed by it
22
Q
Microaerophiles
A
Require O2 in low amounts, but killed by high concentrations
23
Q
Aerotolerant Anaerobes
A
Cannot use O2, but are not killed by it
24
Q
pH
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
