Not using sterile equipment to apply bacteria to nutrient agar plates?

[nadeenjo]

I did an experiment at school, but they couldn't give my group any sterile cotton swabs like we asked so we had applied the bacteria with our bare hands. Now when I am analyzing the results the outcome seems wrong, I was testing the effectiveness of anti-bacterial hand gel and there was more bacteria on the plate with gel. I was wondering if not using sterile equipment affected the results?

[mooeypoo]

I did an experiment at school, but they couldn't give my group any sterile cotton swabs like we asked so we had applied the bacteria with our bare hands. Now when I am analyzing the results the outcome seems wrong, I was testing the effectiveness of anti-bacterial hand gel and there was more bacteria on the plate with gel. I was wondering if not using sterile equipment affected the results?

 

Absolutely.

 

The entire point is that in experiments like these you need to create proper controls to make sure that you test correctly. By not having sterile swabs and by using your hands, you had no proper controls.

 

For instance, it's possible that between the application of bacteria to the "no gel" sample and the "with gel" sample one of you accidentally touched a piece of equipment that had more bacteria on it, or wiped their face, or sneezed, or, even, breathed on the sample and contaminated it.

 

To test this properly, you have to use controls. I'm surprised your school didn't give you any, honestly, but if you have to write your results, you should point out the fact that the lack of sterility makes the results somewhat void, becuse of the possible alternative effects rather than just the gel.

 

~mooey

[nadeenjo]

Thanks I thought so, its a shame really because I was in a physics room they didn't have any "at hand".

[CharonY]

Actually it would have been a simpler experiment if you had just used your finger (without application of additional bacteria) before and after cleaning the hands with the gel.

[DrRocket]

 

...the lack of sterility makes the results somewhat void,...

 

 

Is that something like "somewhat pregnant" ?

 

 

Actually it would have been a simpler experiment if you had just used your finger (without application of additional bacteria) before and after cleaning the hands with the gel.

 

Good idea, so long as one's finger is reasonably dirty to begin with (likely for most folks and almost a certainty for high school students).

[Greippi]

 

Good idea, so long as one's finger is reasonably dirty to begin with (likely for most folks and almost a certainty for high school students).

 

Even if you would consider your finger to be "clean" there's still going to be bacteria living on it, so I wouldn't worry too much about your finger being in a dirty/clean state. Unless, of course, you've just washed with that antibacterial soap...

 

 

Your equipment may be unsterile, but you can also implement other sterile technique - doing it around a bunsen flame, not opening the lid of the plate wider than needed, not breathing on the plate...

Edited January 6, 2012 by Greippi

[CharonY]

The way I understood it, a big issue would also be how the gel was applied. I assume that after that the overall sterility is not really an issue. Also working at a Bunsen, while generally a good idea, can also do more harm than good, if done incorrectly. This is mostly due to the air circulation created by the flame.

[nadeenjo]

Definitely something to think about for next time round thanks for all suggestions.