Chapter 6 - Microbial Growth
1. Describe the physical requirements for microbial growth.
By microbial growth, we mean an increase in the numbers of cells (not the size of individual cells). The physical requirements for growth include the appropriate temperature, pH, and osmotic pressure.
Bacteria are divided into three groups with regard to temperature with each having a minimum, optimum, and maximum growth temperature:
Psychrophiles (cold-loving) - capable of growth at 0oC
do not use oxygen for growth, but is not damaged by it
a complex polysaccharide from seaweed used to make a solid surface for bacteria to grow on
process whereby bacteria undergo cell division and increase in number
organism that grows better at high carbon dioxide concentrations
element which is the structural backbone of all biological molecules
Media that are very precisely prepared for a specific type of culture are known as _______ _______ media.
Media that is less precise because it uses extracts from yeasts, meats, or plants is known as ______ media.
The _____ phase of microbial growth is a time in which the number of microbial deaths exceed the number of new cells formed.
Media which makes it easier to distinguish colonies of the desired organism from other colonies growing on the same plate are known as _______ media.
direct microscopic count
method of measuring bacteria by counting them on a special microscope slide; fast, but there is no way to distinguish living cells from dead cells
used to measure filamentous organisms
A culture that is used to increase very small numbers of a desired organism to detectable levels (often for soil or fecal samples) is known as a/an ________ culture.
can use oxygen when present, but can continue growth by using fermentation and anaerobic respiration when oxygen is absent
does not require a high salt concentration to live, but can grow in the presence of salt up to 2%
method of measuring bacterial cell number in liquid samples when the bacterial counts are expected to be small
The _____ phase of microbial growth is a time of metabolic activity to prepare for future growth.
The _____ phase of microbial growth features exponential growth with a constant generation time.
freeze-drying bacteria for long-term storage
bacteria which grow optimally at 25-40 degrees C; includes most pathogenic bacteria, which grow optimally at 37 degrees C
requires oxygen, but in concentrations lower than that in air
most probable number method
method of measuring bacterial cell number by estimation, based on bacterial growth after serial dilution; useful when bacteria won't grow on a solid surface
requires oxygen to live
unable to live in the presence of oxygen due to the lack of enzymes necessary to neutralize the harmful forms of oxygen
requires a high salt concentration to live
In culturing bacteria, __________ salts are used as a buffer to maintain proper pH.
High solute concentrations cause bacteria to lose water by osmosis with subsequent plasma membrane shrinkage. This process is ___________.
the method of measuring bacterial numbers by counting colonies following serial dilutions; takes 24 hours of incubation, but measures viable cells
bacteria capable of growth at 0 degrees C.
Media designed to suppress growth of unwanted bacteria and encourage the growth of desired microbes are known as ______ media.
The _____ phase of microbial growth is a time during which the growth rate slows as the number of microbial deaths balances the number of new cells.
bacteria which grow optimally at 50-60 degrees C
indirect measurement of microbes by measuring the cloudiness of a solution with a spectrophotometer