Revised Ques. on growing bacteria and variables

[bacteria+petri]

I am trying to conduct an experiment on cell phones and bacteria. I am trying to show that cleaning cell phones with disinfectant can help solve a real world problem of people getting sick from their phone and having to stay home form work and school. I conducted the experiment using one IPHONE 6 which has a large touchscreen. I did this because an experiment should only have one variable and if I used 3 different phones (for three trials) then I would have two variables-- the disinfectant type and the phones. In order to do the experiment on one phone, I marked off 12 squares using thin blue carpenter tape (2 x 2.5 cm). In one square I used a wet nap, in another an alcohol wipe, and a third square I used a clorox wipe. In a fourth square I used nothing at all to disinfect. This was my control. I repeated these procedures 2 more times on the same phone. For Trial 1, I then divided a petri dish into 4 sections (control/alcohol/clorox/wet nap). I swabbed each section of the phone with a clean qtip and wiped it in the corresponding section of the petri dish. I did the same thing for Trial 2 and 3. This was two days ago. Right now it appears there is no growth on 11 out of 12 sections of my petri dishes. The only section I see growth is the control section of the very first trial. I live in a warm climate so I am keeping the dishes on top of the garage refrigerator. I am wondering if the dishes need some light in order to grow colonies? Another question I have is would it be okay to use 3 different phones to conduct three trials? Or am I right that that would be adding another variable? By using one IPHONE, the area to treat and then swab with qtip is very small. It would be so much easier to test only four squares on one phone but use three different phones (for 3 trials total). Any advice for me please?

[SciB]

I would suggest that you do the controls again on the two plates where they didn't grow. This time moisten the swab with distilled water and rub all over the edges of the phone after handling it. Do this the same way for each plate. Keep the plates in the dark somewhere warm--75 to 86 degrees F (24 to 30 C) and leave them there until you see definite colonies in the control sectors.

This is not the scientifically correct way to do your control but it will give you the colonies that are present on a phone that has been handled but not sanitized. As you said, using three separate phones would have been better. You can explain why you did the controls this way in your poster.

For your presentation, take clear close-up photos of each plate. If you want to make a graph, I would suggest creating a scale from zero which represents no growth to 5 which is maximum growth. Score each sector of each plate and then report it as the average of the three plates. This is not a very quantitative way of measuring the effect of the wipers on the microbes but it is the easiest. Showing photos of the plates is good because then people can see the results for themselves.

If you have any more questions about the methods or how to do your poster let us know.

Good luck!

Sybee

[bacteria+petri]

Thank you for your help. You said that using three phones would have been better. I still have time before my project is due and I have 3 phones that I can use. But does that mean I will have 2 variables in my experiment? The type of disinfectant is 1 variable. Is using 3 phones adding another variable because they are different phones? Thank you.

[SciB]

As long as the phones are similar in size and shape they can be considered identical for your purposes, so not a variable.

Be sure you remember to moisten the swabs with sterile distilled water before you use them. Also, take pictures of your procedure as well as of the colonies that grow on the agar. Keep the petri dishes in a warm, dark place while they are growing. It's a good idea to tape the lids to the base of the dish so they don't come off accidentally. Be sure you label the dishes on the sides so the writing doesn't interfere with your photos.

Keep us posted on your progress and if you have any questions at all please ask!

Good luck1

Sybee

[bacteria+petri]

Okay. Thanks for your answer.