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26 Cards in this Set
- Front
- Back
Culture medium
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Nutrient material prepared for growing microorganisms
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Inoculation
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Introduction of a microorganism into medium.
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Culture
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Growth of a Microorganism observed on/in a medium.
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Chemically defined media
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Media when exact composition known
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Complex media
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Media when exact composition varies
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Selective media
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Media that favors the growth of desired microorganisms and inhibits the growth of unwanted ones.
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Differential media
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Media that distinguishes between groups of microorganisms.
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MacConkey's Agar
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Selective medium
1. Inhibits gram-positive bacteria 2. Encourages gram-negative bacteria. Differential medium 1. Lactose fermenters produce acid and form pink colonies 2. Non-lactose fermenters form colorless colonies |
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Blood agar
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Differential media made from 5% sheep blood and the microorganisms change the color of the medium.
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Microbial Growth
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Refers to the increase in number of cells not the size of individual cells.
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Generation time
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The time required for a bacterial population to double (usually 1-3 hours)
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Generation number
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Expressed as a power of 2
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Closed systems
Batch culture |
1. Lag phase: first generation growth time
2. Log phase: exponential growth time 3. Stationary phase: cells are dying as fast as they are growing 4. Decline phase: cells are dying faster than they are growing |
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1. Build up of toxic waste
2. Use up nutrients in a closed system |
Why closed systems always decline
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Continuous cultures
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Open systems
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Direct Methods
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1. Viable plate count
2. Membrane filtration 3. Microscopic count 4. Most Probable Number (MPN) 5. Electronic counters |
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Indirect Methods
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1. Turbidity
2. Metabolic activity 3. Weight |
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Viable Plate Count
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1. Limit CFUs to 30-300
2. Uses serial dilutions Advantages: only living cells Disadvantages: Incubation time Growth requirements May underestimate count |
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Plate count methods
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1. Pour-plates (Good spread of microbes but its hot and can kill them)
2. Spread plates (Not hot but doesn't spread well) |
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Membrane Filtration
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1. Liquid pass through filter
2. Filter placed on solid medium 3. Organisms on filter will grow Advantages: Only living cells Can be used to count low cell concentrations Disadvantages: Must used at least 100 mL of media Incubation time May underestimate count |
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Microscopic Count
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1. Known volume of sample placed in counting chamber
2. Viewed under microscope 3. Cells counted Advantages: No incubation time Disadvantages: Dead cells maybe be counted Tedious Requires high concentration of cells (10 million per mL) |
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Most probable numbers (MPN)
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1. Multi-tube statistical assay
2. Liquid media only 3. Each tube diluted with 10x less sample than previous Advantages: Measure only living cells Useful for culturing cells that wont grow on solid media Disadvantages: Incubation time Expensive and time consuming |
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Electronic Counter
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Coulter counter - electrical current
Flow Cytometry - light transmission Advantage: No incubation time Disadvantage: Dead cells may be counted Not very sensitive due to clumping and other debris in media |
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Turbidity
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1. Uses spectrophotometer
2. Measures light transmitted through sample Advantages: No incubation time Disadvantages: Must have high concentration of cells May count dead cells |
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Weight
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Wet weight - cells centrifuged and packed cells weighed
Dry weight - packed cells dried at 100 degrees C for 8 to 12 hours then weighed Advantages: Useful in measuring filamentous organisms Disadvantages Tedious and time consuming Not sensitive enough Dead cells weighed |
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Metabolic Activity
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Based on enzyme activity
Advantages: Once metabolic rate is established it provides reliable estimate of cell number Disadvantages: Incubation time Requires metabolic rate to be established in advance |