Question:
I am looking for information about effects of bacteria on
meat:
- how electrical features of meat could be changed with bateria
- how to measure /or count bacteria in meat- methodology for measurment of
bacteria in meat.
Replies:
I can't help with the electrical features but you can do what is called a
standard plate count to count the bacteria in meat such as hamburger. Take a
10 gram (weigh it!) piece of burger and put it into 100 mls. of sterile
water. Shake 25 times. Then do serial dilutions. Take one ml of the
mixture and put it into 99 mls of sterile water. This gives you a 1/100
dilution or 10-2 (read as "10 to the minus two"). Take one ml of that
dilution and put it into another 99 mls of sterile water. This gives you
1/10000 dilution or 10-4. Add another 1 ml. to another 99 mls of sterile
water. This gives you a 10-6 dilution. You will need 6 sterile, disposable
petrie dishes and 6 tubes of molten nutrient agar (melted and at 45 deg. C).
Take 0.1 ml of the first dilution and put it into a sterile petrie dish.
Then add the molten agar and swirl until the water is mixed in. Then add 1
ml of the first dilution to a petrie dish and add the molten agar and swirl
the plate. You now have a plate with bacteria diluted 10-1 (1/10) and 10-2
(1/100). Do the same for the other two dilutions of the mixture, putting 0.1
in the first plate and 1 ml in the second plate. You will end up with
dilutions of 10-1, 10-2, 10-3 and so on up to 10-6. Incubate the plates for
24-48 hours or until growth can be seen. The plate that has between 30 and
300 colonies of bacteria on it will be the best to count. Then take the
number of colonies you have and mulitply by the dilution and that tells you
how many bacteria were in the original sample, which was 10 grams of
hamburger. For example, if you counted 45 colonies on the 10-4 plate, you
have 4.5 x 105 in your sample. You can then divide by 10 if you wish to
figure out the number of bacteria/ gram. Good luck
NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.
