What are the 3 critical temperatures for microbial growth and explain the reasons for each. correct answers The 3 critical temperatures define the range suitable for microbial growth.
(1) minimum - membrane gelling; transport processes so slow that growth cannot occur
(2) optimal - enzymatic reac...
MMG 301 - Unit 2 Exam(with accurate solutions)
What are the 3 critical temperatures for microbial growth and explain the reasons for each. correct answers The 3 critical temperatures define the range suitable for microbial
growth.
(1) minimum - membrane gelling; transport processes so slow that growth cannot occur
(2) optimal - enzymatic reactions occurring at maximal possible rate (max growth rate)
(3) maximum - protein denaturation; collapse of the cytoplasmic membrane; thermal lysis (denature enzymes and proteins; membrane fluidity breakdown)
Optimal temperatures varies widely; can be near 0 degrees celsius for some organisms,
or 106 degrees celsius for others
Explain the effect of temperature on the kinetics of sterilization by heat correct answers Contents of autoclave gradually heat to set temperature of 121 degrees celsius at 15 lb/in^2 pressure for a minimum of 15 minutes.
- high pressure prevents boiling of liquids
- the high temperature, not the high pressure, kills microbes
- slow cooling while maintaining pressure prevents boiling of liquids
How do the survival curves for thermophiles and mesophiles differ? correct answers Decimal reduction times are longer for thermophiles and shorter for mesophiles.
Create a temperature vs. time graph for a typical autoclave sterilization cycle correct answers Temperature = in chamber of autoclave
down slope = cool slowly / gradually
Know the typical temperature and time of exposure for an autoclave sterilization. correct
answers Typical temperature is 121 degrees celsius at 15 lb/in^2 for a minimum of 15 minutes
Describe how the correct functioning of an autoclave can be tested correct answers Validation of proper autoclave operation can be done by including pre-packaged bacterial spores + indicator growth medium in autoclave cycles.
Performed on a routine basis on all autoclaves at a facility. No growth (color will remain purple)
Growth, pH change (color will change)
Explain why acidity is useful for preserving certain foods correct answers In food preservation, high salt and acidic pH are often used together. Microbes can tolerate high salt concentrations by synthesizing internal solutes to balance water availability. Compatible solutes are non-toxic osmolytes that are synthesized inside the cell to balance water activity outside the cell. Nonhalophiles (low NaCl), Halotolerant, Halophile, Extreme halophiles (no growth below
10%)
Acidity is often used as a method of food preservation because it inhibits growth of many harmful microbes.
Why do some batch cultures grow better if a pH buffering agent is included? correct answers 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
What results from placing a microbe in a hyperosmotic or a hypoosmotic environment? correct answers 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.
growth rate vs. salt concentration graph (identify nonhalophile, halotolerant, halophile, and extreme halophile) correct answers What are some compatible solutes and how are they utilized by halophiles? correct answers Compatible solutes are non-toxic osmolytes that are synthesized inside the cell
to balance water activity. Examples: Sucrose and Dimethylsulfoniopropionate
Halophiles accumulate a restricted range of highly soluble low molecular weight molecules termed compatible solutes, which helps them to cope up with environments of elevated osmolarity.
Review the major groups of aerobic and anaerobic microorganisms. correct answers Aerobic: Obligate Aerobe, Microaerophile, and Facultative Anaerobes
- Obligate aerobe: must have O2 to grow
- Microaerophile: only grows in low O2 concentrations
- Facultative: prefer O2, but can use other pathways for energy
Anaerobic: Obligate Anaerobe and Aerotolerant anaerobe
- Obligate anaerobe: cannot grow if O2 is available
- Aerotolerant anaerobe: grow in air but does not use O2
Explain how aerobic and anaerobic microorganisms can be distinguished using thioglycollate-resazurin agar. correct answers Oxygen preferences for a pure culture can be determined using thioglycolate agar tube cultures. Thioglycolate creates an oxygen gradient in the tube while resazurin turns red in the presence of oxygen. Cells will grow in different areas of the tube depending on where oxygen is present allowing for aerobic and anaerobic microorganisms to be distinguished.
What do the thioglycolate and resazurin components do? correct answers Thioglycolate
agar medium = agar + sodium thioglycolate + resazurin
Thioglycollate = reacts with oxygen and creates an oxygen gradient in the tube
Resazurin = turns red in the presence of oxygen These two components determine the oxygen preference of a microbe.
cardinal temperatures correct answers the minimum, optimal, and maximum
Microorganisms can be categorized according to their temperature range for growth. correct answers psychrophile: -5-15 degrees celsius
mesophile: 15-45 degrees celsius thermophile: 45-80 degrees celsius
hyperthermophile: above 80 degrees celsius
decimal reduction time correct answers time to reduce viable cells 10 fold
extremophile correct answers microbe that survives extreme conditions (pH, temp., salt concentrations)
water activity correct answers the vapor pressure of air over solution divided by the vapor pressure of air over pure water
describe pasteurization and two ways this process is typically done correct answers A heating method that is intended to reduce numbers, but not kill all microbes; short-
duration heating method that is used on heat-sensitive liquids.
Batch method: product is heated for a short period and then coded (ex. 63 degrees for 30 minutes)
Continuous Flow: product rapidly heated and then coded while moving through heat exchanges (ex. 72 degrees for 15 seconds followed by cooling to 4 degrees celsius)
provide examples of biological damage caused by ionizing radiation and UV light correct
answers Radiation exposure results in time-dependent accumulated damage that eventually kills cells and viruses.
Ionizing radiation (gamma rays): damage to DNA and proteins via electrons and radicals (ex. sterilization of medical devices, foods, meat, and pharmaceuticals)
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