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10 Cards in this Set

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What are two ways of plating diluted bacterial samples?
-transfer 0.1 ml a sample to center of sterile agar plate and use sterile hockey stick to spread
-transfer 0.1 ml sample to melted agar tube and mix: pour this onto another solid plate and swirl it
How long are plates incubated for dilution tests?
-24 hours at appropriate temperature
How do you find the CFU's of a plate?
-count the colonies and locate the "countable plate" (30-300)
How do you find the SDF of a dilution problem?
-this is the initial sample or flask (sample dilution factor)
-if undiluted it would be 1/1
-if 1ml substance is diulted with 9 ml water, the SDF would be 1/10
How do calculate the individual tube dilution factor (ITDF)?
-vol transferred/(vol sample transferred + volume diluent)
-example: 0.1 transferred to 9.9ml would be a 1/100 ITDF
How do you find the Total Seris Dilution Factor (TSDF) for a countable plate?
-multiply ITDF's up to tube used
*do NOT use tubes that came AFTER the countable plate since it wasn't part of the dilution!
How do you find the Plating Dilution Factor (PDF)?
-divide amount transferred by 1 ml
*always compare this to 1ml!
Why do you always compare the plated amount transferred to 1 ml?
-because original concentration is CFU/ml
How do you find the Final Dilution Factor?
-SDF x TSDF x PDF
How do you find CFU/ml in ORIGINAL sample?
-CFU of countable plate x 1/FDF OR
-CFU/FDF