Expert: Dana Krempels, Ph.D. - 5/15/2010

Question
Hi, I am doing a project for my 10th grade biology class and I was wondering if you could help. It's a science experiment and I cooked meats to different temperatures, then incubated the bacteria  [with agar]. I was testing the rate of decrease in bacteria as cooking temperature increases.


I found out that the bacteria does not decrease linearly as the cooking temperature increases (the first 20 degrees increased killed more than the next 20 degree increase). At 100 degrees, nearly all the bacteria was wiped out. However, there were some (very small amount) left. Since I am doing my project around food safety, I was wondering- How do thermophilic bacteria work (what makes them more resistant to heat)? Do you know of any implications this has for food safety?

Thanks in advance!

Answer
Dear Jean,

It's not possible to know what the specific mechanisms of heat tolerance are in the bacteria you have without doing a culture to find out what they are.  But many heat tolerant organisms have chaperone proteins that help prevent denaturation of vital enzymes at higher temperatures.  You can read more about that here:

http://en.wikipedia.org/wiki/Heat_shock_protein

However, if this was a very fast heating, the bacteria may not have had time to upregulate the expression of any heat shock proteins they might make; it's possible they have them at the ready all the time.  

Alternatively, it's quite possible that the few bacteria that did grow on your agar from the high temperature medium were contaminants, and that there actually were no survivors.  If you do enough replicates with *very* meticulous technique, you will be able to determine if this is the case.

Good luck on your project!

Dana