Term
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Definition
| cold loving microbes (<15ºC) |
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Term
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Definition
| microbes that thrive in average temps (15-45 °C) |
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Term
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Definition
| Heat loving microbes (45-80 °C) |
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Term
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Definition
| extreme heat loving microbes (> 80 °C) |
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Term
| psychrotolerant eurymesophiles |
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Definition
Some microbes (eury-) tolerate an extended range of
temperatures; e.g., psychrotolerant eurymesophiles can grow at 4° C and therefore are largely responsible for food spoilage at refrigerator temperatures; thermotolerant
eurymesophiles spoil food in hot vending machines. |
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Term
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Definition
The three critical temperatures for a specific microbe
- minimum - the microbe doesn't grow below this temp
- optimal - the temp range the microbe will grow
- maximum - the microbe doesn't grow above this temp
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Term
| Decimal reduction time (D) |
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Definition
| The time required at a certain temperature to kill 90% of the organisms being studied. |
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Term
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Definition
used for milk and other heat-sensitive foods to reduce the population of undesirable microbes; involves heating to 66°C for 30 min (batch) or 71°C for 15 sec (continuous flow) |
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Term
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Definition
| thrive in acidic conditions (~pH 2) |
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Term
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Definition
| thrives in neutral conditions (~ pH 7) |
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Term
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Definition
| thrive in alkaline conditions (~ pH 10) |
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Term
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Definition
| an organism that thrives in and may even require physically or chemically extreme conditions that are detrimental to the majority of life on earth |
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Term
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Definition
Some microbes are obligate acidophiles
or alkalinophiles, unable to grow at
neutral pH 7 |
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Term
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Definition
vapor pressure of air over substance or solution divided by the vapor pressure of air over pure water
- can categorize microbes into certain water activity ranges they grow in
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Term
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Definition
| an environment where the solute concentration is much higher outside the cell than inside. Causes plasmolysis. |
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Term
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Definition
loss of water and collapse
of internal structure |
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Term
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Definition
Microbes experience the hypoosmotic stress when exposed to very low external solute concentrations (E. coli gut --> river); periplasmic oligosaccharides counterbalance, murein
sacculus maintains protoplast integrity so cell doesn’t burst. |
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Term
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Definition
| to be adapted for life with limited supply of water |
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Term
| what are the three critical temperatures for microbial growth? |
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Definition
Cardinal temperatures
- minimum
- optimal
- maximum
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Term
| review kinetics of sterilization by heat |
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Definition
•There is an exponential rate of death upon exposure to heat that is dependent on two
factors:
•Heat
•Time |
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Term
| how do the survival curves for thermophiles and mesophiles differ? |
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Definition
| at a given temperature, the decimal reduction time is higher in thermophiles than mesophiles |
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Term
| how is Pasteurization performed on heat-sensitive foods |
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Definition
| either a batch is heated to 66oC for 30 mins or in a continuous flow mechanism, the substance is heated to 71oC for 15 seconds |
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Term
| why is acidity useful for preserving certain foods? |
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Definition
| because in certain foods with natural acidity (lemon juice, vinegar), microbes don't grow. |
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Term
why do some batch cultures grow better if a pH buffering
agent is included? |
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Definition
| sometimes microbes produce waste products that can change the pH of the surrounding environment to the point where the microbes can't grow. A pH buffer will prevent these pH changes |
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Term
| what results from placing a microbe in a hyperosmotic environment |
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Definition
plasmolysis: In this case, the water concentration is higher within the cell, water leaks out --> the protoplasts dehydrates and shrinks, Metabolism slows down considerably without available water. |
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Term
| what results from placing a microbe in a hypoosmotic environment? |
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Definition
| too much water diffuses into the cell and causes the cell to lyse |
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Term
| how are compatible solutes utilized by halophiles? |
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Definition
Microbes adapt to osmotic imbalances using compatible solutes: non-toxic osmolytes that can accumulate to high concentrations within cells to counterbalance adverse
osmotic effects of high external solute concentrations. |
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Term
| amino acid type compatible solutes (2) |
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Definition
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Term
| carbohydrate compatible solutes (2) |
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Definition
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Term
| review the major groups of aerobic microorganisms |
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Definition
• Obligate: require O2, tolerate 0.21 pO2
• Microaerophilic: require O2, tolerate ≤ 0.02 Po2
• Facultative: OK with / without O2, use aerobic
respiration with O2, anaerobic respiration
or fermentation with no O2 |
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Term
| review the major groups of anaerobic microorganisms |
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Definition
- Obligate: does NOT tolerate O2
- Aerotolerant: OK with / without O2 but only use anaerobic respiration or fermentation (no aerobic respiration)
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Term
| how can aerobic and anaerobic microbes be distinguished using thioglycollate-resazurin agar |
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Definition
Classification of O2 tolerance based on position of
microbial growth in semisolid tube agar deeps containing
Na thioglycolate and resazurin: Turns pink after prolonged exposure to O2
- See Fig. 6.27 in lecture 16
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Term
| what method is used to validate the proper functioning of autoclaves? |
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Definition
- Include pre-packaged samples of Bacterial endospores– test for growth after each sterilization cycle
- Indicator strips that change color at high temperatures
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