Good vs. bad bacteria

[deleted-171069]

All of my students are required to do an in-school science fair project. This year, many have chosen topics that involve growing bacteria. I really want them to try to determine if the bacteria on their petri dishes is 'good' or 'bad' bacteria. I have researched this quite a bit but have yet to come up with a test (or a chart or a resource) that can help identify if the bacteria colonies in the dishes are good or bad. Any suggestions or leads are greatly appreciated!

[deleted-352009]

Hi mallison,

Unfortunately, without access to lab testing or a microscope, it's very difficult to accurately determine whether bacteria are "good" or "bad." Additionally, without proper protective equipment, opening the Petri dishes to try to test bacteria is not recommended, since it's very easy for pathogenic bacteria to escape and cause health issues.

However, you could try asking each student to identify the common strains of good and bad bacteria that commonly exist on the surface they're growing bacteria from. For example, if a student were taking swabs from the inside of the human mouth, lactobacillus and streptococcus are often present. Then, students could look at photos of colonies of each of the types of good and bad bacteria and compare these to the colonies in their Petri dishes. However, this test probably won't be completely accurate.

Hope this helped,
Allison

[deleted-352784]

All of my students are required to do an in-school science fair project. This year, many have chosen topics that involve growing bacteria. I really want them to try to determine if the bacteria on their petri dishes is 'good' or 'bad' bacteria. I have researched this quite a bit but have yet to come up with a test (or a chart or a resource) that can help identify if the bacteria colonies in the dishes are good or bad. Any suggestions or leads are greatly appreciated!

Hi mallison,

I am so glad that many of your students are getting a head start on learning about bacteria and microbiology!
As for determining whether the bacteria your students have grown on petri dishes are 'good' or 'bad', students could accomplish this in different ways.
Your students could be instructed to recognize different harmful and dangerous (pathogenic) bacteria and see if the bacteria that they have grown match. (A chart could be made listing different pathogenic bacteria and their characteristics.)
For example, on this website: https://www.sciencebuddies.org/science- ... ates.shtml , in the 'Bacteria' section, Bacillus subtilis is shown on a nutrient agar plate. If the student's agar plate has the same characteristics as B. subtilis, the student can assume that their bacteria isn't harmful (since B. subtilis lives in the soil and has been determine not to be pathogenic/disease-causing).
Another way students could differentiate good and bad bacteria is by identifying the bacteria through different tests, such as gram-staining or acid-fast staining (many gram negative bacteria are more pathogenic than gram positive, and acid fast bacteria are mostly pathogenic).
Acid Fast staining: http://www.microbiologyinfo.com/acid-fa ... -examples/
These tests may be difficult to conduct for your students, however. Making a chart of different pathogenic bacteria and their characteristics would be a much easier way for students to visually tell on their petri dishes if their bacteria are harmful or not.
Hopefully this helped!

Sincerely,
JSK