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7 Cards in this Set
- Front
- Back
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What is a quick way to measure the number of bacteria in a culture? What equipment do you use? How does it measure the number of cells? Why is it just an estimation? |
Measure turbidity or cloudiness of a broth culture using a spectrometer. Cell concentration is inversely proportional to amount of light passing through culture. The amount of light blocked is the optical density. Turbidometic reading only give a rough estimate because it measures dead cells as well. Plus O.D. values can only be interpreted after calibrating them to the absorbance values of concentrations determined by standard plate counts. |
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What assumption do we make when we count the number of colonies on the plate? |
We assume that one colonie arised from one cell. |
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What are two ways to perform the standard plate count? Describe each. |
The pour plate technique involves preparing a series of dilutions then mixing some of the diluted culture with molten agar before pouring it onto a plate. The spread plate technique requires the spreading of the diluted culture onto a prepared agar plate so the cells are on the surface of the plate. |
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We only counted plates between numbers ... because otherwise they are... |
We only count plate between 30 and 300 colonies because that gives us the most reliable results. Otherwise we call them TNTC (>300) or TFTC (<30). |
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How do you perform a serial dilution of a culture? |
Tranfer 0.1ml of culture into the blank labelled 10e-2. Transfer 1.0ml of dilution into 10e-3 blank. Same for 10e-4, -5 -6 and -7. Pour molten agar in plate and gently mix. Allow to solidify. Do same for other plates. |
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Why do we use the colony forming unit (CFU) instead the term 'cell' when expressing density of of the orgamism? |
Because colonies could arise from multiple cells |
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How do you calculate the number of organisms per ml in the original culture? |
Divide the the number of colonies by the dilution factor will give tou the number of organisms in original culture. |
