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Organisms that are likely to be encountered in low-temperature food spoilage because they grow fairly well at refrigerator temperatures
Microbes that have an optimum growth temperature of 80 degrees celsius or higher
Organisms that do not require high salt concentrations but are able to grow at salt concentrations up to 2%, a concentration that inhibits growth of many other organisms
A chemical element (mineral) required in small amounts for growth, such as iron, copper, molybdenum, and zinc
Aerobic bacteria that have developed, or retained, the ability to continue growing in the absence of oxygen
Singlet oxygen (1^O2-)
Normal molecular oxygen (O2) that has ben boosted into a higher-energy state and is extremely reactive
A toxic form of oxygen (OH.) formed in cytoplasm by ionizing radiation and aerobic respiration
An organism that does not use molecular oxygen (O2) but is not affected by its presence
Organisms that are aerobic (require oxygen) but grow only in oxygen concentrations lower than those in air (small amounts of oxygen).
Media contain ingredients such as sodium thioglycolate that chemically combine with dissolved oxygen and deplete the oxygen in the culture medium
Media that suppress growth of unwanted bacteria and encourage the growth of the desired microbes
Media that make it easier to distinguish colonies of the desired organism from other colonies growing on the same plate
Culture medium used for preliminary isolation that favors the growth of one particular microorganism but not others.
Streak plate method
A method of isolating a culture by spreading microorganisms over the surface of a solid culture medium
Process in which a pure culture of microbes is placed in a suspending liquid and quick-frozen at temperatures ranging from -50 degrees C to -95 degrees C
A suspension of microbes is quickly frozen at temperatures ranging from -54 degrees C to -72 decrees C, and the water is removed by a high vacuum (sublimation)
Bacteria form a small initial outgrowth (a bud) that enlarges until its size approaches that of the parent cell, then it separates
Log phase/exponential growth phase
When the cells begin to divide and enter a period of growth, or logarithmic increase
Period of equilibrium in which the growth rate slows, the number of microbial deaths balances the number of new cells, and the population stabilizes
Death phase/logarithmic decline phase
When the number of deaths eventually exceeds the number of new cells formed
A method of determining the number of bacteria in a sample by counting the number of colony-forming unites on a solid culture medium
Colony-forming units (CFU)
Plate counts that count the short segments of a chain of bacterial clump; don't assume each live bacterium grows and divides to produce a single colony like a plate count
Pour plate method
A method of inoculating a solid nutrient medium by mixing bacteria in the melted medium and pouring the medium into a Petri dish to solidify
Spread plate method
A plate count method in which inoculum is spread over the surface of a solid culture medium
The passage of a liquid or gas through a screenlike material; a 0.45- µm filter removes most bacteria
Most probable number (MPN) method
The greater the number of bacteria in a sample, the more dilution is needed to reduce the density to the point at which no bacteria are left to grow in the tubes in a dilution series.
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