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The pour plate differs from the streak plate in that the agar medium is inoculated while it is still liquid , but cooled to 45 degrees Celsius, and colonies develop throughout the medium, not just on the _____.


The idea is to make successive _____ of the cells and then on at least one of the poured plate colonies will be separated well enough to see them as isolated.


Move quickly; because..
If the medium ____ in the tube, remelting kills the organisms and re inoculation is required.

pure culture

grow from well isolated colony (no contaminants)

mixed culture

will show different types of colonies

pour, spread, quadrant streak

Name the three ways to isolate colonies.
1) _____ plate
2) ____ plate
3) ____ ____

serial dilutions

several dilutions of same volume in a row

quantitative dilutions

Serial dilutions AKA....


Pour plate:
Add inoculum to plate then pour agar on top and gently _____ plate.


Pour Plate:
Inoculum must be ____ culture

skill, separation

Pour Plate Advantages:
- Less ____ than streak methods
- May provide greater _____

reculturing, concentration, seen

Pour Plate Disadvantages:
1) most colonies grow below surface;
- difficult to access for _____
2) surface growth appears different than subsurface growth
3) difficult to get the right ______ of cells/plate for counting (30-300)
-Which means do multiple plates (different concentrations)
4) species with low numbers of colonies may not be _____


Exercise Protocol:
Work in groups of 2-3 to complete the procedure
Very important to follow directions and work _____
- Read protocol carefully
- Do not write directly on bottles
*label w/ tape & remove when done

plates, flame

Exercise Protocol:
- Prepare everything ahead of time
* Label everything and put inoculum in ____ before getting agar out of the water bath
- Wipe water and condensation off of agar tubes (even under lid), then ___ tube rim before pouring
* Make sure there is nothing growing in the tube
- Swirl gently to mix; leave on bench until solid
- Incubate 37°C


Pipets should only be used _____ at a time.

multiples, bench top

Pipets should NEVER:
1) Be removed in _____
2) Placed on a ____ ____ before or after use

direct method

plate count from pour plate

indirect method

count with spectrophotometry


The direct method always involves ___.


Surface growth appears different than subsurface growth
- So be sure to count ____colonies

colony forming units

CFU stands for


A measure of viable cells in which a colony represents an aggregate of cells derived from a single progenitor cell.

estimated, original

- CFU is an ____ measurement
- Correlation of number of colonies to the number of bacteria in _____ culture

average, 30, 300

Count colonies on each of duplicate plates and _____
-choose dilution w/ ___-____ colonies

Quebec colony counter

If too many colonies to easily count, use ____ ____ ___;
-Petri plate is 56cm2
-count 4 squares (1cm2)
-average the counts from 4 squares
-multiply by 56 to get total for plate (56 cm2)


-Take colony count X _____ of dilution factor for the plate that was counted
Ex. 238 colonies counted from plate with 1 ml of 10-8
238x108 CFU/ml
2.38x1010 CFU/ml


The measure of the amount of light absorbed by a suspension of bacterial cells or a solution of an organic molecule with the use of a colorimeter or spectrophotometer.

surface, subsurface

The streak plate method involves streaking the culture across a sterile agar gel surface. In the pour plate method, agar in a molten state is poured over the sample, and the plate is then inverted. The streak plate therefore produces only _____ colonies, whereas the poured plate shows those colonies AND _____colonies both on and within the agar layer.

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