Science Buddies: "Ask an Expert"

I am working on the third phase of a water filter experiment. Phase 1 found that a combination of sand and gravel worked best to filter dirty water. Phase 2 found that activated charcoal worked best to filter and make water taste better. Phase 3, will test to see which type of light will be most effective in killing bacteria in water. I have been trying to find a mentor to work with at our local university (FIT). So far, I have word that they have received my information and will contact me soon. My school has advised me to go ahead & order supplies. Do you know where to get pre-infected agar plates with bacteria that I can use to infect the water for my experiment? Thank you for your help, 6th Gr Student

I doubt that any individual can buy pre-infected agar plates anywhere. Some firms sell beneficial bacteria for acquarium use; however, those may not be appropriate for your purposes. Most places that do research with bacteria cultures maintain tight control over their own strains. You really need to be working with a mentor for this aspect.

Thank you for replying. I have been unable to ask anything of my mentors yet as they have not contacted me. Thank you for letting me know.

Hi Dama - I have some additional information for you from our lead scientist at Science Buddies.

First, she suggests that the following information may be useful:

1) Look at this PI https://www.sciencebuddies.org/science- ... p025.shtml and follow how it gets bacteria
2) Bacteria cultures can be purchased at Carolina.com but may need to be ordered through your school. E. coli K-12 is a good non-harmful strain to use (http://www.carolina.com/bacteria/escher ... a+cultures)

She also notes the following:

Things for the student to think about: Using live bacteria (even ones marked harmless) always means you need to be careful and follow basic microbiology procedures.

• Do NOT drink any of the water that may have bacteria - no matter how good you think your filtering system is.
• Read our Microorganism Safety page https://www.sciencebuddies.org/science- ... fety.shtml
• Double check with your teacher/science fair that using bacteria is okay within the science fair rules. Sometimes fairs have special forms and rules that apply. The rules for ISEF-related science fairs are detailed here: https://www.sciencebuddies.org/science- ... _src.shtml

I hope this helps.

Amy
Science Buddies

Thank you for your reply, Amy. I won't be doing anything with the bacteria we order until I have a mentor. The school wanted me to order the supplies and build the third phase of my filter so I wouldn't be so behind. But I won't be doing anything else until I have a mentor. We have been waiting and they said they would return the forms. I hope with your information the school can order the bacteria and as soon as we hear from the mentor I can get started. Thank you very much for all the information, Dama

Hi Dama,

Are you doing a project similar to this one on the Science Buddies website? This is a very challenging project, but it sounds like you have already done a lot of work and have some great results. Amy and Craig have given you some really good suggestions for this project and I am including a suggestion for your experiment.

https://www.sciencebuddies.org/science- ... #procedure

To test the effectiveness of various lights on bacteria, you need to start with a water that contains some bacteria, and then expose samples of the same sample to light and count the bacteria before and after to find out which light worked the best.

Since you have not found a mentor to work with you, you can try the following.

1. The K-12 E. coli that Amy suggested would be an excellent choice for a safe bacterium to work with. If you transfer a small amount of this organism to a sample of sterile beef broth or other clear culture medium and incubate it until it just turns cloudy, you can assume that the sample will contain about 10,000,000 bacterial per mL. You might be able to use milk that has just spoiled as an alternative. This type of sample would contain a mixture of bacteria that would grow easily and would be very unlikely to contain anything pathogenic.

2. Next, get a gallon of distilled water and boil it to kill any bacteria that might be present. Do not use tap water as this will contain chlorine that will inhibit the growth of bacteria. Add 8 drops of the E. coli culture to the gallon of water after it has cooled completely. This will give you a sample containing about 1000 bacteria per ml. Expose samples of the water to light and reserve one sample as a control (you will have to use sterile containers to hold the water). Transfer two drops (or 100 uL if you have a pipette) of each sample to the surface of the agar plate and spread the sample over the surface of the plate with a sterile cotton swab. Invert the plates and incubate them in for 2-3 days. Count the colonies and compare the results with the control sample.

It would be good to test a 1:10 dilution of each sample also and do duplicate samples, but you may be limited in the number of plates available. If you have time, do the experiment twice.

Before you start this part of the experiment, read the rules for doing projects with potentially hazardous biological agents. It sounds like you have permission from the teacher to do the project, and I think that if you seal the plates and don't open them after they have incubated your project will comply with the rules.

https://www.sciencebuddies.org/science- ... ents.shtml

Also, read the information on microbiological safety, sterilizing glassware, and incubating plates from the Science Buddies website. This information should be useful to you.

https://www.sciencebuddies.org/science- ... ques.shtml

I don't know what types of supplies you have ordered, so let me what type of medium you will be getting if you need an alternative suggestion, or if you have any other questions.


Donna Hardy