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27 Cards in this Set
- Front
- Back
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Microbial Growth
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Refers to an increase in the # of cells, not the size of a cell.
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Mother (Parent) Cell
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Duplicates its contents and doubles in size
Divides into 2 daughter cells |
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Cell Division
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Occurs by binary fission or budding
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Binary Fission
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Most bacteria...
- Cell duplicates its components and divides into two cells - Daughter cells become independent when a septum grows between them and they separate |
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Budding
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Mainly in Yeast
- A small new cell develops on the surface of an existing cell and subsequently separates. |
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Bacterial Cell Division
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Prokaryotic cells do not have a cell cycle with a specific period for DNA synthesis
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Bacterial Cell Division (2)
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Continuously dividing cells replicate the single bacterial chromosome shortly before division
Chromosome is attached to the cell membrane - Grows and separates the replicated chromosome |
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Bacterial Cell Division (3)
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Cell temporarily may have 2 nucleoids
May have incomplete seperation - Diplo, strepto, tetrads, sarcinae, staphylo - Some always form the above shapes, some do so under certain conditions |
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Phases of Growth (l)
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Lag Phase
-organisms do not increase in number, but are metabolically active |
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Phases of Growth (2)
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Log Phase
-Once organisms are adapted, population growth is exponential or logarithmic -cells are dividing at their most rapid rate -Best time to identify Bacteria shape |
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Phases of Growth (3)
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Generation Time
- the time it takes to double the population - can vary from 20 minutes to 20 hrs most are under 1 hr |
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Phases of Growth (4)
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Stationary Phase
- as growth increases exponentially, nutrients are used up, resources get tight, new cells are produced at the same rate as cells die off, numbers stay constant |
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Phases of Growth (5)
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Death Phase
- conditions worsen, the number of live cells decreases at a logarithmic rate Involution - Cells assume unusual shapes, difficult to identify, pleiomorphic - Never do stains on an old culture, best to use log phase growth |
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Serial Dilution
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Successive 1:10 dilutions of a liquid culture are made and then transferred to an agar plate to grow and be counted
- Direct microscopic counts - Most probable number technique - Filtration - Measurement of turbidity - Measurement of metabolic products - Dry weight |
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Phases of Growth: Solid Media
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Colony
- a group of descendants of an original cell - after growing exponentially, the organisms at the edges continue to divide rapidly while the ones in the middle stop growing or die |
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Phases of Growth: Solid Media (2)
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All phases of the growth curve occur simultaneously in a colony
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Physical Requirements for Growth
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pH
Temperature Oxygen Moisture Hydrostatic pressure Osmotic pressure |
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Moisture
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A must for bacteria, only spores survive in a dry environment
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Barophiles
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Bacteria that must have high pressure in order to live
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Neutrophiles
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between pH 5.4-8.5
most pathogens |
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Acidophiles
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between pH .1-4
Lactobacillus; Helicobacter pylori (Single most cause of ulcer) |
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Alkaliphiles
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between pH 7.0-11.5
Vibrio Choleraie grows at pH 9 |
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Temperature
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- Minimum, optimum, and maximum temperatures
- Optimum temperature for growth is usually near the maximum temperature |
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Psychrophiles
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Grow just below 0 degrees Celsius-20 degrees Celsius
Obligate - cannot grow above 20 degrees Celsius |
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Mesophiles
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Most bacteria
25-40 degrees Celsius |
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Thermophiles
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Grow best at 50-60 degrees Celsius some as high as 110 degrees Celsius
Obligate only about 27 degrees Celsius Facultative above and below 37 degrees Celsius More common than psychrophiles Grow well at refrigerator temperature (Do not actually grow well at the low temp, but grows better than others) Cause low-temp food spoilage Over time degrade food Most microbes survive even subfreezing temps |
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Food Spoilage
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Oxygen Metabolism
Obligate aerobes Facultative anaerobes Microaerophiles Obligate anaerobes Facultative Anaeroves Aerotolerant anaerobes |
