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Micro 6.2

What are the two common methods of preserving bacterial cultures for long periods? Deep-freezing and lyophilization
What is deep-freezing? method where a pure culture of microbes is placed in suspending liquid and quick-frozen.
What's the range of temperatures for deep-freezing? -50 to -95 degrees Celsius.
After deep-freezing, how long is the microbe preserved? For several years.
What is lyophilization? Freeze-drying.
What happens during lyophilization? A suspension of microbes is quickly frozen and the water is removed by a high vacuum.
What is the temperature range for lyophilization? -54 to -72 degrees Celsius.
lyophilization: what's done to the container while the water is removed by the vacuum? The container is sealed by melting the glass with a high temperature torch.
How do the organisms remain after the deep-freezing process? After lyophilization? Deep-freezing leaves a block of ice. Lyophilization leaves organisms in a powder-like residue.
How long can the microbes be stored after lyophilization? How are they revived? Decades. Can be revived by hydration with a suitable liquid nutrient medium.
What's the definition of generation time? The length of time it takes for a cell to divide and for its populations to double. (on multiple choice as well! Answer on there is written as simply "The length of time it takes for a cell to divide")
What are the 4 DIRECT methods of measuring microbial growth Plate count, filtration, the most probable number (MPN) method, and direct microscopic count.
What does a plate count reflect? the # of viable microbes. Assumes that each bacterium grows into a single colony.
How are plate counts reported? as colony-forming units (CFU)
What are the 2 methods of doing a plate count? 1. pour plate method 2. streak plate method
What happens during filtration? bacteria are retained on the surface of a membrane filter and are then transferred to a culture medium to grow and subsequently be counted.
What is the most probably number (MPN)? What kind of microbes can it be used for? It's a statistical estimation that can be used for microbes that will grow in a liquid medium.
How are microbes counted in a direct microscopic count? the microbes in a measured volume of a bacterial suspension are counted with the use of a specially designed slide.
What are the 3 INDIRECT methods of measuring microbial growth? Turbidity, metabolic activity, dry weight.
What's used to determine turbidity? How does it work? A spectrophotometer. Measures the amount of light that passes through a suspension of cells.
What does the metabolic activity method assume? That the amount of metabolic product (like acid, or CO2) is in direct proportion to the # of bacteria present. (there's only as much poop as there are people, after all)
What do you do during the dry weight method? Extract, filter extra material, & dry it in a desiccator. Weigh.
Created by: Erushi Amaya Erushi Amaya