Ever wondered what germs are on your kid’s hand after playing in your backyard? Tasha Sturm, mother of two, decided to find out. Sturm, who works as a microbiology lab tech for Cabrillo College in Aptos, California, made a sample of her son’s handprint in a Petri dish after he played outside and pet the family dog. She used an agar plate (a sterile Petri dish lined with substance used to grow bacteria), and described the process here:
Tryptic Soy Agar (TSA) can be purchased through a number of companies (Fisher Scientific, Hardy Diagnostics, Neogen). Most sell it in the powdered form, add water, autoclave, cool to about 55 degrees then pour into the plate, cover with the lid then let solidify. Once the plates are cool then place the hand on the plate making sure to gently pressing the fingers/palm to make contact with the agar. Cover the plate with the lid and place in a 37 degree C incubator for 24-48 hrs……incubate agar side up. This will grow the normal flora on the hand like Staph., Micrococcus, etc. Take the plate out and let it incubate/set out with the lid on at room temp (22 degrees C) for several days (3+ days). Normal flora will continue to grow (slowly) and yeast/fungi will start to grow….usually colored colonies (red/pink/yellow). It will also help bacteria like Serratia turn red. Once grown the plate should be treated as a Biohaz and disposed of properly. The plate should not be opened if mold/fungi is present without proper respiratory protection.
After about a week, the handprint had exploded into colorful designs. But what are these mysterious bacteria on her 8-year-old’s hand? Sturm thinks the white circle at the bottom right may be Bacillus, while the other white spots may be Staphylococcus and the yellow-orange may be yeast.
“It’s normal stuff that we’re exposed to every day. The skin protects us from a lot of the bad stuff out there,” Sturm said to TODAY. “The take home message is that to have a healthy immune system, you’ve got to be exposed to stuff.”
If you’re looking to learn about the bacteria on your family’s hands, further instructions can be found here!
And make sure you remember– although this DIY lesson is fun and informative, it’s important to keep track of your hygiene. Here are details on the right way to wash your hands.