MICRO Chp 6 Flashcards
What are the two main types of requirements for microbial growth?
Physical requirements and chemical requirements
Physical requirements involve environmental conditions like temperature, pH, pressure, and light intensity. Chemical requirements involve the presence of specific elements or compounds.
What is the optimum growth temperature?
The temperature at which an organism grows best
It is different for different organisms.
What are the three broad groups of microbes based on temperature preference?
- Psychrophiles
- Mesophiles
- Thermophiles
What is the optimum growth temperature range for psychrophiles?
0°C to 15°C
Strict psychrophiles have an optimum growth temperature of 15°C, while psychrotrophs prefer 20-30°C.
What is the optimum growth temperature range for mesophiles?
25-40°C
Most spoilage and pathogenic microbes are mesophiles.
What are thermophiles’ optimum growth temperatures?
50-60°C
Some Archaea are hyperthermophiles with optimum temperatures of 80°C or higher.
What pH range do most bacteria prefer for optimal growth?
pH 6.5 – 7.5
Acidic products of metabolism can inhibit growth by lowering pH.
What are acidophiles?
Microbes that prefer acidic conditions (pH 4 or lower)
Molds and yeast prefer slightly acidic conditions for optimal growth (pH 5 – 6).
What is the preferred water concentration for most microbes?
About 99%
Higher or lower concentrations can lead to cell rupture or excessive water loss.
What are obligate halophiles?
Microbes that require high salt concentrations to function
Some obligate halophiles can function at water concentrations as low as 70%.
What are autotrophs?
Microbes that use carbon dioxide from the air
Capnophiles prefer higher levels of CO2.
What are obligate aerobes?
Microbes that require oxygen to survive
What is a biofilm?
A community of microbes in thin layers on various surfaces
Biofilms can contain multiple species and have heightened resistance to antimicrobial agents.
What is a culture medium?
Nutrient material used for microbe growth
What is an inoculum?
Microbes added to a culture medium to initiate growth
What is a chemically defined medium?
Culture medium where the exact chemical composition is known
What is a selective medium?
Culture medium designed to optimize growth for specific organisms
Other organisms do not grow as well or at all in selective media.
What is a complex medium?
Culture medium without an exact chemical composition
Contains complex ingredients like digested proteins and yeast extract.
What are fastidious organisms?
Organisms that require complex media to survive
What are the four distinct phases of microbial growth?
- Lag phase
- Exponential growth phase
- Stationary phase
- Death phase
What is generation time?
The time required for the live cell number in a culture to double
What does turbidity measure?
The cloudiness of the culture medium
The more opaque the medium, the higher the microbial population.
What is the most probable number method?
A statistical process of estimating microbial population
What is dry weight measurement?
Removal and drying of microbes, and measurement of mass
