Oscillator

The Results! Part 2

The past few days I’ve been learning a lot about the bacteria that surround me and realizing just how labor intensive an actually well-controlled handwashing experiment can be! Here is a little bit more of the data I’ve collected about bacteria on everyday objects:

i-ca270443ba8d718623a157790a9ba3f4-stuffonplates-thumb-510x149-48657.pngDusty corners (unsurprisingly?) have the most bacteria, followed by chewed gum, then pens and computer mice. These data also show that the medium of bacterial transmission has a huge effect on what shows up on the plate. Leaving the actual object on the plate–in this case a dust bunny–allows for a lot of bacterial transfer, as does transfer through a liquid via the chewed up gum.

This medium-dependence also affects the handwashing experiments. One of the comments on the last post mentioned a microbiology class experiment of touching plates immediately before and after hand washing, where invariably the after washing would have more bacteria because of the moisture on the hands allowed for better transfer. My data show the same result:

i-8f84a6be68dc8a65dd8b4ecdb99724d6-handsprepost-thumb-510x362-48659.pngThis rules out the hypothesis that bacteria is introduced by the towel used to dry my hands, and since I already tested the water for bacterial contamination during the aquapocalypse I know that there’s no bacteria that can grow on plates in the water either, so this bacteria is coming from my hands and transfers to the plate easier through the water. I’m still surprised that thirty minutes after washing had so much bacteria last time, the experiment needs repeating to see whether this trend is consistent, to make sure that my hands weren’t accidentally damp for some other reason leading to more bacterial transfer, and to see how my activity during the day affects the bacteria (last time I washed my hands right before lunch and then touched plates consecutively approximately every thirty minutes).

Other experiments I want to try are washing with Purell or other kinds of explicitly “antibacterial” soaps (I was using the “gentle” soap from VWR “for frequent washing” and washing much more thoroughly than I usually do), and to also try touching plates that have antibiotics in them to see if any of the colonies are also antibiotic resistant. There are of course so many species of bacteria that won’t ever show up on plates. Initiatives like the Human Microbiome Project can begin to explore these bacteria through sequencing, which doesn’t require bacterial growth in culture (and is of course way beyond the scope of my experiments!)

People have been engineering the ecology of their microbiome for thousands of years, eating foods with live microbial cultures on purpose like yogurts and cheeses. As we understand more about the populations that live with us in a detailed way we can understand how they contribute to our health and immune system, learn to appreciate them and perhaps even learn to re-engineer them.

Comments

  1. #1 Art
    May 10, 2010

    Interesting post.

    I used to work in a hospital and one of the people I used to lunch with was in charge of a section of their sterile supply. Her conclusion, and this was back in the 80s, was that sterility was largely an illusion because if you culture carefully enough with the right media you can get positive results off of anything.

    Even things that had been smothered in ethylene oxide and blasted with superheated steam. Items that were said to be ‘sterile’.

    I think she was ahead of her time because she hinted that perhaps instead of trying to kill off all the germs, and seeing massive blooms of whatever shows up first, we might do better to saturate the things we come in contact with with friendly germs so the items essentially defend themselves against the noxious varieties.

  2. #2 Jeffrey Bary
    May 10, 2010

    Perhaps you should blow-dry your hands with (sterile) air directly after washing and then again at the 30 minute mark.

    But now you’re stuck with making sterile air.

  3. #3 JerryM
    May 11, 2010

    You’ve officially got a fan now :)

    I also don’t think sterile is important in this string of experiments. My question was mainly about seeing what happens on your hands after washing, in a real world scenario. People go to the bathroom, wash their hands (hopefully?), dry them with whatever’s around, and go on with their lives. They’re not doctors scrubbing for 5 minutes holding up their hands before putting on gloves even (what’s that about anyway? what are the gloves for?).

    Do you have any ability to see what kind of bacteria are on the plates?

  4. #4 JohnV
    May 11, 2010

    One bonus of the gloves is that it keeps you off of the doctor :P