akiria
Posts: 3
Joined: Thu Nov 18, 2010 8:22 pm

### How can I measure bacteria?

I'm doing a science project on how does liquid soap affect the growth of bacteria. I'm going to have several jars with chicken broth,something, and liquid soap. But one jar will not have any liquid soap. For my project my independent variable is the liquid soap and the dependent variable is the bacteria. Thing is I have to be able to measure the bacteria cause its my dependent variable. And I have no idea how to measure it. So if you could please help me with how to measure it I'd be very grateful. Also I'm wondering if I mixed up the variables and liquid soap should be the dependent and bacteria the independent.

barretttomlinson
Former Expert
Posts: 932
Joined: Wed Oct 03, 2007 12:24 am

### Re: How can I measure bacteria?

Hi,

Here is a Science Buddies Project Writeup that describes measuring bacterial content of various liquids:

http://www.sciencebuddies.org/science-f ... 5&from=TSW

For help on doing the project you may want to consult the Science Buddies Project Guide:

http://www.sciencebuddies.org/science-f ... ndex.shtml

For help on variables in particular, read the project guide page on variables:
http://www.sciencebuddies.org/science-f ... bles.shtml

Good luck and ahave fun with the project!!!

Best regards,

Barrett L Tomlinson

akiria
Posts: 3
Joined: Thu Nov 18, 2010 8:22 pm

### Re: How can I measure bacteria?

Thank you. One more question though. Is it possible to put it in units? Because one of my teachers questions is "What data will you collect? (Units- think metric!)"

sciencediplomat
Former Expert
Posts: 32
Joined: Fri Aug 13, 2010 8:27 am

### Re: How can I measure bacteria?

Hello Akiria
If you are referring to what unit is used in measuring bacteria the answer would most commonly be micrometers (µm).
If you have any more questions just ask and good luck!

donnahardy2
Expert
Posts: 2671
Joined: Mon Nov 14, 2005 12:45 pm

### Re: How can I measure bacteria?

Hi Akiria,

Science diplomat is correct; if you measure bacteria under a microscope, you would measure them in microns. However, it sounds like you are going to be counting the number of bacteria in various solutions, so you would be measuring number of bacteria per milliliter.

Did you read through all of the links that Barrett gave you? The information on the science buddies website is excellent. Since you will be measuring bacteria for the first time, I recommend that you do a trial experiment with one solution to develop your technique. If you will be measuring bacteria that have been growing for a while, you should know that the bacteria will be as high as 10,000,000 organisms per ml, so you will need to plan to do dilutions so you will be able to do accurate counts.

Please let us know if you have any more questions.

Donna Hardy

Former Expert
Posts: 137
Joined: Tue Sep 18, 2007 5:06 pm
Occupation: science journalist

### Re: How can I measure bacteria?

The standard units microbiologists use for what you're measuring is called CFU--colony forming units, measured per ml or whatever volume you're interested in. Each bacterium, presumably, will form one colony on an agar plate.
Amber Dance
Science Buddy

akiria
Posts: 3
Joined: Thu Nov 18, 2010 8:22 pm

### Re: How can I measure bacteria?

So I talked to my teacher and she suggested using perti dishes to measure the bacteria. I've looked around but I haven't been able to find out how to use the petri dish or how to put the bacteria on it.