Blog Post #3: Mysterious Microbes

I chose to sample some “traditionally” dirty surfaces, a computer keyboard, the inside of a door handle, a toilet seat, and a phone screen. I expected growth on all four of the surfaces, especially since keyboards and (at least this door handle, judging from the amount of grime on the swab) the inside of doorknobs are rarely cleaned. On day 3, there were no visible cultures in the doorknob, keyboard, or phone screen samples, and some small dots of culture in the sample obtained from a toilet seat. On day 7, there were still no signs of life on any of the samples except for the toilet seat, which had bloomed with droplet-like drops of white, yellow, and orange. Unsurprisingly, the toilet seat was full of bacteria that survived well in an agar medium, but shockingly enough, none of the other surfaces grew so much as a lone bacterial outpost on the petri dish. Given the amount of biological material that has the potential to pass by a toilet seat, it follows that it would have the best chance of at least harbouring a bacteria that grows well in agar medium, but I expected a regular and thorough cleaning would at least somewhat take care of that. In any case, I would keep using the paper toilet seat covers in the upstairs men’s bathroom. On the other hand, computer keyboards are (hopefully) only touched by people’s hands, and rarely disinfected, so I expected as much if not more bacterial growth on that sample, but either hands rarely have bacteria that thrive in laboratory environments, or people’s hands really are that much cleaner than whatever parts make their way across the men’s toilet seat.

On Brian’s petri dish of samples from sink faucets, all of the surfaces tested grew bacterial colonies that were of similar individual size and colour. In order of increasing colony size, the areas tested were the front of the hot water sink handle, the front of the cold water sink handle, the back of hot water sink handle, and the back of the cold water sink handle. Both of our plates were similar in that the only samples that grew colonies were from moist environments (sink handles and toilet seats), although the bacterial colonies from the sinks were flatter and “splotchier” than the round colourful domes that grew from the toilet seat. The faucet colonies however all grew much further apart than the toilet communitites. Both of our dishes also sampled from areas that are both routinely touched by hands: faucet handles, door handles, and computer keyboards – but again, only the samples that were in wet environments grew colonies. This could of course just have to do with Brian being better at getting samples from the surfaces themselves, and less to do with the surfaces themselves, but as both of our procedures were identical and used the same kind of swabs, sanitized water, and petri dishes, this should be minimized.

The experiment revealed to me that while we know from literature that microorganisms are everywhere, that doesn’t mean that they can all grow on agar plates in a lab. Of the surfaces that did grow cultures in petri dishes (the sink faucets and the toilet seat), all of them were also moist environments in addition to constantly being touched. This could have to do with the fact that the petri dishes themselves were moist environments, strongly encouraging the growth of the microorganisms that thrive in this particular climate.

     Are dry environments absolutely more sterile than moist environments or are there plating techniques or conditions that would encourage growth of samples from drier areas over moist ones?

     How effective really is sterilization of surfaces in a bathroom? Does it make a difference by the time you get back to your class? Will different amounts of routine cleaning in a public bathroom result in much cleaner hands once outside?

    Since both faucets and toilet seats contain more bacteria that grow in laboratory conditions than the other surfaces tested, will the faucets in the bathroom contain more bacteria of that type than both surfaces combined?

     The faucets in the lab and the toilet seat in the men’s bathroom both contained many microbes that grew well in laboratory environments, and both environments are much more damp than the other samples tested. This is due to the fact that the microbes that prefer a damp environment grow well in laboratory conditions and not due to them harbouring more microbes, since all of the surfaces tested were considered “dirty.”

Petri dish at 3 days of growth

Petri dish at 7 days. Toilet seat sample only one with any growth.

Brian’s petri dish at 7 days.