Does wearing black socks create more bacteria than white?

[lassolin000]

I'm pretty sure that wearing black socks creates more bacteria than wearing white socks. To test my hypothosis I'm having my test subjects wear one black sock and one white sock for a day, then use petri dishes and agar to collect and grow the bacteria samples. How would I collect the bacteria? Should I use a cotton swab to get some from the inside of the shoe, then touch it to the agar, or should I have the subjects, like, dip their toe in the agar, etc.? Does this kind of project need a control, and if so, what? This is actually my first science fair project and I must admit, I've basically been winging it so far and I need some advice. It's due in two weeks (1-21-14).

[pseizure]

I would use a water bath. Dip the sock in some water then collect the water for spreading on agar for CFU counts. You'd need to work out the details as this is just an idea. What makes you think black socks have more bacteria?

And yes it needs a control. This would be unused black and white socks.

[SciB]

Hi,

Definitely an unusual subject for a science project! I might have suggested comparing feet in socks to feet without socks, but in winter this is probably not practical unless you live in Miami.

The bacteria are going to be growing on the feet not on the socks, so i would use sterile cotton-tipped swabs to take 'samples' from between the big toe and the next toe and maybe from the ball of the foot and apply these to an agar plate. Have your friends do this immediately after removing the socks and have everyone wear them for the same number of hours. You can't control where they go or what they do while they are wearing one black and one white sock, but you might warn them to be prepared with some answers when quizzical people ask them why! "Oh, it's just so i can tell my right foot from my left."

Since you are comparing feet from the same person, the only control would be wiping a clean swab on the plate just to prove that the swab itself has no bacteria on it. The statistical question is how many people do you need to test to get valid data and i can't answer that one for you. As usual, the more people you test, the more likely you will get statistically significant results. One thing you will have to be sure and do, however, is make sure that all the socks are identical except for color. In fact, what i would do is buy a bunch of cheap white cotton socks and dye one of them black so that way they would be all the same weight and density. You don't want some people wearing cotton socks and some wearing polyester or a combination.

Keep us posted on this fascinating project. I think I'll try it myself and see if there is a difference!

Good luck,

Sybee

[lassolin000]

Awesome, thanks! I'll let you know how it goes!

I only have two petri dishes currently, and enough agar for one experiament in each. Would it mess it up if I did all the black sock bacteria in one petri dish and all the white sock bacteria in the other, or should I just order more dishes and agar?

Oh, and pseizure, I think black socks will grow more bacteria because of the heat factor; black traps heat much better than white does, and bacteria grows best in damp, warm places.... right?

[SciB]

Hi,

How many feet are you going to test? The more people you test, the better your statistics will be so try to get as many as possible. As for the agar plates, you should order more. I wouldn't do more than two tests per plate, so you should have one plate for each person--one for the foot with the black sock and one for the foot wearing the white sock. Wear rubber gloves to swab the feet and to apply the samples to the plates. Try to swab the feet in exactly the same way each time so that you get a uniform sample. Plan ahead of time which areas you will swab and for how long and stick to this procedure exactly.

Be sure you read the instructions on using bacteria safely: https://www.sciencebuddies.org/science- ... fety.shtml

Dispose of the swab in a small tightly capped bottle of 10% Clorox that you bring with you. It is also a good idea to tape the lid down to the plate with masking tape so it doesn't come off by accident. If it does then the results with that plate are invalid. Remember to incubate the plates with the lid down so that any moisture condensing on the top won't run down onto the plate and spread your samples.

It is going to be difficult to actually measure a difference in amount of microbes on the plate because you may just get a smear of colonies where you swabbed the agar. Also keep in mind that bacteria aren't the only bugs that grow on feet. There are some pretty bad fungi that can cause athlete's foot and toenail disease, so be very careful handling the plates after the colonies have grown up. I would not even open them. Just take pictures through the top. When you are done with all the plates, get a pail big enough to submerge them in and fill it 3/4 full with a 10% solution of Clorox bleach. Put the plates and lids in there and let them sit overnight. Then you can seal them up [wear gloves!] and dispose of them in the trash.

Also remember that human foot microbes would grow best at a temperature that is greater than room temp, about 21C, but not as warm as the internal temp of 37C. I would guess around 30C would work. So, how do you do that? You can make a simple incubator (see the attached pdf file) using an incandescent [not fluorescent] light bulb, a box and a thermometer. The instructions are for using a 20 gallon aquarium but a sturdy cardboard box would work as well. Try different watt bulbs till you get the temp inside to stay at 25-30C [77-86F]. Be careful not to make it too hot or the microbes may not grow at all. Some organisms grow fairly quickly and others take their time, so don't be in a hurry with the plates. Let them incubate long enough to get a good growth of colonies before you take pictures. Again let me emphasize--LEAVE THE LIDS TAPED ONTO THE PLATES! There are some dangerous human pathogens that can grow on this agar so always wear nitrile or latex gloves when handling the dishes and don't open them!

Good luck and do let us know how your experiment turns out.

Sybee

[lassolin000]

Oh No!!!!! What am I going to do? I mixed my agar with the right proportions, let it sit in the fridge for the allotted amount of time (1 hour) but it didn't set up and turn into a gel like it was supposed to. My subjects and their bacteria were all ready and waiting, and it was time to go to bed and them to go home, so I went ahead and swabbed their feet and dipped them in the thick liquidy agar. Will it still grow any bacteria, or is it a complete failure? It's a little runnier than syrup. I was going to turn them upside down like I was recommended to do to avoid condensation, but predictably, the liquid runs to the bottom (the lids). HELP!!!!!

[yvetteds]

I am not sure exactly how you prepared the agar.
But even if it didn't set into gel when you introduced the bacteria, if bacteria are present in the solution you will see the colonies after the agar sets.

As a matter of fact, that is exactly what happens if when you are making the agar solution for an experiment and accidentally introduce bacteria into the solution because of sloppy procedures - you will see colonies when you didn't expect to.

[SciB]

Sorry to hear about the problem with the agar. Did you use 15 grams per liter as recommended?

Anyway, as Yvette said, the bacteria will grow in the syrupy agar but they will be harder to photograph.

Definitely DO NOT turn the plates upside down!!

It is a good idea to seal the tops of the plates to the bottoms with some tape because once you put the swabs into the agar and the bacteria have grown DO NOT open the plates. Some of these bacteria and fungi are very harmful and you don't want to expose yourself to them. Use Clorox on the plates when you are done to kill the microbes.

Do you have a warm, dark place to let the bacteria grow? The closer you can get to 37C, the human body temperature, the better. Make sure you put them where any family members, particularly young ones, will not disturb them.

Check the plates once a day and let them grow until you see some definite colonies in the agar. They may be white, yellow or even red depending on the species of bacteria. Take good, sharp close-up photos and print them in color for your presentation.

You did remember to do a control swab alone with NO bacteria as a control, right?

We are all curious about the results, so please do let us know when you have the final pictures.

Good luck,

Sybee

[yvetteds]

Thanks for the most important reminder -- to keep the plates taped closed - never open them - once colonies start growing you don't know if they are 'good' or 'bad' - and now they are concentrated in a small environment, could be a health hazard.

I hope you have followed all the safety procedures for handling bacteria; gloves; sterile technique; and that you know how to dispose of your materials when you are finished with your experiment. You do NOT just throw them in the trash!

Please make sure your science teacher has provided you with the safety procedures for this experiment.

Also, even if the agar never 'sets' you might still be able to salvage some observations for results -
Compare the control plate (agar; no introduced bacteria from subjects) to the experimental plates.
If not 'set' you can compare the clarity or cloudiness of the agar. When bacteria grow - the more - the more cloudy the agar will appear compared to your control.

If you had more time - you could use these plates as a source to plate out a new set of agar plates. This time being very careful to follow directions when preparing the plates. One of the easiest ways to be sure of good results is to purchase ready made culture plates from one of the scientific companies - your teacher can direct you.

You are learning a lot - even if it doesn't work out perfectly the first time - this is what science is all about - discovery!

Have fun with it and keep us posted!