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Old 10-25-2005, 01:33 PM
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Post This might help!!!

Determine the effect of incubation temperature on bacteria growth rate ?

Materials needed

4 Incubators
12 Plastic test tubes
18 Petri dishes
My bacteria
1 Moist plastic bag
Broth that supports the bacteria growth
A Data sheet
1 Pair of latex or vinyl gloves
1 Fluid impermeable lab coat
1 Nephlometer
2 Micro liter measurers (10 and 20 uLs)
1 Density measurer


1) Take two Petri dishes and remove the lids

2) Set one of the dishes in a kitchen and one in bedroom

3) Let them collect bacteria for one hour

4) After an hour place the lids on the dishes

5) Place the dishes in a moist plastic bag and seal

6) Take to a hospital and have them analyze the bacteria and place each collected sample in a separate prepared broth that supports their growth

7) Let the bacteria grow enough so that you can work with it for your experiment

8) Divide the two cultures of bacteria into 2 tubes each and add more broth

9) Label those tubes 1-4
Conduct Temperature Trials:

10) Place 12 test tubes on a tray in 4 rows of 3.

11) Label the first tube in each row 1, 2, 3, 4.

12) Pump 1. 8 ml. distilled water into the first test tube in the 1st row

13) Take a cotton swab and remove some bacteria out of the #1 sample of bacteria.

14) Swish the swab around in the water of the first test tube in the 1st row

15) Measure and adjust turbidity of test tube contents on an electronic density measurer so that it has 80% light transmission.

16) Take 20 micro liters (uL) of the solution in the first test tube in the 1st row and place it in the second test tube of that same row

17) Add 1. 8 ml. distilled water to the second test tube.

18) Take 20 microliters (uL) of the solution in the second test tube in the 1st row and place it in the third test tube of that same row

19) Add 1. 8 ml. distilled water to the third test tube.

20) Repeat steps 12-19 to the remaining 3 rows, except use only the respective bacteria for that row (for example, bacteria sample #3 is only used for test tubes in row #3)

21) Sort 16 sterile Petri dishes into groups of 4 and label each group with a number, 1-4. Within each group additionally label each dish with one of four temperatures to be tested: 42 C. , 37 C. , 20 C. , 5 C.

22) From the third test tube of row #1 draw 10 uL of the diluted bacteria and place into a Petri dish labeled #1. Do this four times total, once for each temperature group: 42, 37, 20, 5.

23) Spread the bacteria around the plate in 3 directions (vertically, horizontally, and diagonally) with a plastic loop.

24) Repeat steps 22 and 23 with the diluted bacteria from the other 3 rows being sure to place bacteria in the respectively numbered Petri dishes.

25) Place the Petri dishes in the four incubators at the temperatures specified on each dish.

26) Leave them in the incubator for 6 days

27) Take the Perti dishes out immediately after that time

28) Count the live bacteria colonies with the use of a magnifying glass (if
necessary) or the unaided eye.

29) Record the number on a data sheet

30) After all the bacteria tests have been done kill all the bacteria you have worked with. They must be autoclaved.
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