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Science Sunday: UV Light vs Bacteria

While looking for a project for this year’s science expo (or science fair as it is called in the States), I came across the most fascinating thing. Airports use UV light hand-dryers in their restrooms.  Now admittedly I do not frequent airports as I rarely fly anywhere so I have not witnessed this first-hand but as we all know the internets never lie *cough cough*. Upon further investigation it became evident that some beauty salons and hairdressers also employ UV light to sterilize their tools.  Another quick search with my good friend Google revealed numerous devices of a UV nature for sale to the general public. Yep you can now sterilize your cell phone in this manner as well.

Being the skeptic that I am I desperately wanted to find out if UV light can actually be used as a sterilization tool. My friend and I who worked on this project together decided to test on yeast because it is a unicellular microscopic organism which translated to English basically means that it is “weak”. We reckoned that if the UV light was not effective on a single cell organism such as yeast then it would probably not be effective on bacteria and viruses that are more resilient. Also we figured that there was no way thirteen year olds would be allowed to test on E-coli.

A bit more on yeast then:  Yeast is part of the fungus family and when yeast has something to feed on like sugar and also has oxygen, it buds. Basically it reproduces. When yeast is just sitting around in your cupboard it is certainly alive but is unable to bud.

The yeast cultures after incubation

Our method was as follows: In order to culture the yeast we mixed it in some sugar water, put it into 3 glass bottles and left it in  a dark cupboard for 2 days. We took the yeast cultures to the lab at WITS University (the lab at school does not have  equipment  advanced enough for this type of experiment) where we transferred the yeast to agar plates. Each plate was  allocated a specific  time ranging from 10 seconds to 20 minutes. We put each plate on the UV lamp according to their  allocated time and after all  that had been done we transferred the yeast that had been exposed to UV light onto potato dextrose  agar plates. These cultures  were incubated in a warm room for 2 days. Upon our return the yeast had flourished into thousands  of bread smelling growths all  over the plates.

We observed that even on the 20 minute exposure the yeast cultures were thriving however we did notice that the growth was   substantially less than what we found on the plates that had been exposed for shorter periods.

Now for the skeptic bit. Our findings does not bode well for all the people out there who thought their hands were being effectively sterilized when using the UV hand dryers for less than a minute. It is clear that for UV light to be effective one would require extensive exposure to its rays. This also begs the question: How long do beauty salons expose their tools for? We do however know that in hospitals the UV lights are kept on constantly increasing its efficacy.Considering our findings we are pretty much convinced that long term exposure would be effective as a germicide. As far as short-term exposure goes I doubt I will be purchasing a personal UV device anytime soon. Also, do we absolutely have to kill all the bacteria, most of which is harmless, at the risk of weakening our immune systems? But this of course is another topic for another day.

Oh and if you were wondering, yesterday at the Eskom Expo for Young Scientists we were awarded a gold medal for our efforts







Featured Image Credit: Shehal

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Xe'nedra is a pre-teen free thinker who can often be found with her nose in a book. She is an expert at rolling her eyes and making her parents sigh in exasperation. Skateboarding and golf is on her list of sporting activities and she would love to study Forensics or Medicine (which is better than being Gwen Stefani which was her aspiration at age 3). She also blogs as "The Sceptic Kid"

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