MadSci Network: Microbiology

Re: What is the best way to test for bacteria around my high school?

Date: Tue Sep 28 10:54:54 1999
Posted By: Michael Benedik, Faculty Biology and Biochemistry, University of Houston
Area of science: Microbiology
ID: 937101960.Mi

This is certainly something that can be easily done. You are going to need 2 
things. First, you need some petri dishes with culture medium so that the 
bacteria can grow. There is no single medium on which every bacteria will 
grow, but some good all purpose medium like Nutrient agar will do well and 
allow many different bacterial species to grow fine.

The second thing you will need is something to take your samples. This can 
be little swatches of cloth or paper disks (filter paper cut into squares or 
circles), or even Q-tips (cotton swabs) will work well. However whatever you 
use needs to be sterile. The simplest thing to do is to  wrap a bunch in 
aluminum foil, and sterilize them. If your school has an autoclave, that will 
work great. If not, you could put them in a pressure cooker for 30 minutes. If 
you can't do that, put them in an oven at around 300-350 for an hour or so. 
BE CAREFUL that there is nothing plastic, which will melt and make a mess. 
Only paper or cloth. NOTE: Some brands of q-tips have wood sticks, some have 
paper (white), and some have plastic (usually blue but sometimes white).

In order to take your samples, carefully remove one swatch or swab without 
touching the surface you are going to use to collect the bacteria. It would 
be best to wear disposable plastic medical gloves (you can get these at a 
drug store). Rub the swab along the test surface then rub it on top of an agar 
plate. Repeat for each test site. Be sure to do a control where you just rub a 
swab on the agar plate without touching anything, to see what your background 
level will be from the air and your hands.

This is the experimental design. However just doing the experiment is not 
enough. You have to design a hypothesis that you are testing and then test 
it in a controlled way so that you can interpret your results. Otherwise you 
will just get a bunch of numbers that don't really tell you anything. So 
come up with your hypothesis first, then decide how to design an experiment 
that will test your hypothesis and either support it or disprove it.

Have fun!

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