Science Buddies: "Ask an Expert"

How can I test the bacterial content in water and identify the bacteria at a reasonable cost?

Thanks for your help!!

monanejad wrote:How can I test the bacterial content in water and identify the bacteria at a reasonable cost?

Thanks for your help!!

Okay, three things.

1) Culturing bacteria can be dangerous, so please read the safety precautions/ discuss with your science teacher!

2) Look at the microbiology section of the project ideas at:
https://www.sciencebuddies.org/mentorin ... ?from=Home
Some specific methods are at :
https://www.sciencebuddies.org/mentorin ... ?from=Home

(but read the safety warning at the bottom of :
https://www.sciencebuddies.org/mentorin ... roBio_p007)

You can easily modify the methods.

3) Lastly- think carefully about your sources of water- most tap water is heavily chlorinated and probably won't show any results. You probably want a source that does show bacteria, so you can prove your method works! Showing a bunch of agar plates with no bacteria could mean no bacteria or that you kill them all!

As for identifying the bacteria, you could sort them by physical characterstics (as suggested in the labs above). Identify a particular type by name (E. Coli or whatever) is much more complicated. You might want to check in the Life Sciences forum and see if anyone has any cheap methods. I think though, generally DNA testing is used as the definitive test, while visual idenitication and staining (Gram's stain) is used to provide a starting point. See for example: http://www.scienceteacherprogram.org/bi ... han97.html (I got this by searching for "identifying bacteria" at google.)

If you use these methods, be sure to include the proper reference in your report.

Good luck!
Louise

For a cheap, simple method to identify functional groups (aerobes, denitrifiers, iron reducers, etc), I would recommend reading about Most Probable Number (MPN) techniques. They do not require a lot of expensive equipment.

Acridine orange direct counting is another popular technique. I can provide more info if you want.