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19 Cards in this Set
- Front
- Back
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direct cell counts
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Usedto determine total number of cells; can be used for those bacteria that cannotbe cultured
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Two types of direct cell counts
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Directmicroscopic countCellcounting instruments
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Direct microscopic count
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Rapid, but at least 10^7 cells/ ml mustbe present to be effectively counted. Counts include living and dead cells
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Cell- counting instruments
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Coultercounters and flow cytometers count total cells in dilute solutions. Flowcytometers can also be used to count organisms to which fluorescent dye or tagshave been attached.
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Viable cell counts
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Usedto determine the number of viable bacteria in a sample, but only include thosethat can grow in given conditions. Requires an incubation period ofapproximately 24 hrs orlonger. Selective and differential media can be used enumerate specific speciesof bacteria.
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Types of viable cell counts
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Plate count
membrane filtration most probable number |
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Plate count
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Time-consuming but technically simplemethod that does not require sophisticated equipment. Generally used only if the sample has atleast 10^2 cells/ml
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Membrane filtration
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Concentratesbacteria by filtration before they are plated; thus can be used to count cellsin dilute environments
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Most probable number
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statistical estimation of likely cellnumber; it is not a precise measurement. Can be used to estimate numbers ofbacteria in relatively dilute solutions
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Measuring biomass
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biomass can be correlated to cell number
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Ways to measure cell biomass
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Turbidity
Totalweight Chemicalconstituents |
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Turbidity
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very rapid method; used routinely. A one-time correlation with plate counts is required in order to use turbidity fordetermining cell number.
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Total weight
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Tediousand time consuming, however, it is one of the best methods for measuring thegrowth of filamentous microorganisms
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Chemical constituents
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Usechemical means to determine the amount of a given element, usually nitrogen.Not routinely used
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Measuring cell products
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Methodsare rapid but must be correlated to cell number. Frequently used to detectgrowth, but not routinely used for quantitation
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Ways to measure cell products
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Acid
Gases luminescence |
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Acid
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titration can be used to quantify acidproduction. A PH indicator is often used to detect growth
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Gases
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Carbondioxide can be detected by using a molecule that fluoresces when the mediumbecomes slightly more acidic. Gases can be trapped in an inverted durham tubein a tube of broth.
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Luminescence
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Fireflyluciferase catalyzes light- emitting reaction when ATP is present
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