specific number of bacteria

[monanejad]

Is there any wasy to get a specific count of the number of bacteria in the mouth?

[MaryamM]

Well, it is impossible to count the number of bacteria in the mouth directly, but what you could do is make a solution of bacteria from the mouth, dilute it, and then count the number of bacterial colonies.

To do this, take a sterile swab and rub the insides of the cheeks (or palate, teeth, etc., depending on what surface of the mouth you are concentrating on). Take the swab and inoculate a tube of sterile broth with it. Use the method of serial dilution (http://biology.kenyon.edu/courses/biol0 ... ution2.htm) to dilute that initial culture. Take 0.1mL from each tube and inoculate a petri dish with it. Just remember that by taking 0.1mL of culture from the tubes, you are further diluting the concentration of bacteria from the tube by 10X. Incubate the petri dishes for 48 hours and then count the number of bacterial colonies in the dishes that have between 30 and 300 colonies. Multiply the number of colonies by the dilution factor to get the number of bacteria in the initial culture. Be sure to do more than one trial!

What exactly is your project on? What grade are you in? If you tell me, I may be help you do some more with this project.

Hope this helps. Best of Luck!

~Maryam M.

[deleted-71615]

When you quantify bacteria, the most common technique use in microbiology lab is the inoculum counter-streak.

http://mmi.creighton.edu/Manuals/Lab%20Manual1_2.htm

(Figure 2 urine culture method)

Michael

[monanejad]

I am in 11th grade, and my project is on the effectivness of different forms of the substance, xylitol, in the mouth. It has been proven to neutralize pH and prevent cavities. I hope to find out which method of administering the substance is most effective (gum, mint, mouthwash, etc).
Thanks for your help!
Mona

[deleted-71670]

So the way I see it, you have two possible routes:

1) Do a lab-based, outside-the-mouth experiment. You would get some bacteria (I would suggest just using standard E coli) and treat them with the xylitol in a dish or test tube. Then, the way to figure out how many there are in a solution is a technique called "serial dilution"--look that up along with "bacteria" and I think you'll find lots of how-to descriptions.


2) But I can tell what you really want to do is a more direct experiment of bacteria in the mouth, after chewing gum or using mouthwash. Be careful with this, some science fairs have regulations about what kinds of bacteria you can culture from the human body. You could potentially grow something pretty nasty.
I guess one possibility is to have your subjects swish a standard amount of water around in their mouths for a standard amount of times, then spit it out and do serial dilutions of that. I'm not confident that this would give you really trustworthy results.
I once taught a microbiology lab that involved a little experiment where students spit into a tube, and the tube had a color indicator in it. It started out green and the more yellow it turned, the more bacteria you had (or something like that--I don't remember the exact details). Then, you could rate how yellow the tubes turn after different treatments, and this would give you semi-quantitative results. I am trying to find out more about how that experiment was done, I'll post again if I can get more details.

One thing to note is that different people have more or less hospitable mouths for bacteria. So you would want to use several different subjects.

I hope this helps, let me know if anything is unclear.

Amber

[deleted-71670]

The test I was thinking of is called a Snyder agar deep. If you Google those words you'll find some instructions. I'm afraid I have no idea where to obtain the stuff, you could ask your teacher or maybe try Carolina Biologicals. Please post again if you need more info on the technique.

---Amber