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im doing a science fair project to test the five second rule. i want to count the bacteria that grows on the food after it was dropped. I will test 10 seconds 20 seconds 30 seconds and 40 seconds for each type of food. i just need to know how to count bacteria
The project will go SOMETHING LIKE this..
http://books.google.com/books?id=eoCPznKeBL8C&pg=PA26&lpg=PA26&dq=sciece+fair+5+second+rule&source=web&ots=Rzt7WoectM&sig=cM7tRhcX5-biD6txr4zNkd4t3AY#PPA27,M1

2007-11-12 04:13:57 · 1 answers · asked by thatgirlyouknow 1 in Science & Mathematics Botany

omg im only 14 years old how in the world do i know this...use smaller and simpler words please! i need this!

2007-11-13 11:45:59 · update #1

1 answers

Since you are streaking the swab across the plate the colony forming bacteria should be well distributed. Do not hesitate to sweep the swab across the entire plate surface to ensure the bacteria are transferred and spread. Use a light continuous sweep back and forth in an S shape. Do not cross back over an area already touched just one long S. If you just dab the swab on the agar the colonies will be less likely to transfer and may be so close they grow together.

The bacteria you pick up on the food will be in colony forming units (CFUs). Some bacteria will not be alive so will not form a colony. Others will be in sticky clumps so form only one colony. You will need to count colonies not the total number of bacteria in each colony.

You calculate back from the number of colonies you see on each plate. The number of colonies is divided by the sample area to give bacterial concentration. You will need to measure the cracker & the banana's areas before you dispose of them.

There are problems with swabbing the bacteria from the food onto the agar plate. The bacteria may not transfer completely so your count may not reflect actual floor numbers. Make note that it would be better to make a suspension of the food, do a serial dilution, and plate from the total volume of suspended bacteria.

Another way would be to place the swab in medium and gently agitate briefly to suspend the bacteria. Then plate the medium. This may require equipment you do not have access to but should be noted as part of the research on the experimental procedure.
http://www.science-projects.com/serdil.htm

2007-11-12 09:05:49 · answer #1 · answered by gardengallivant 7 · 0 0

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