Help with science fair method.. pretty please :)

[sonna10]

hi everyone

im doing my science fair on "do essential oils inhibit oral bacterial growth?"

im testing tea tree oil , eucalyptus, cinnamon, clove , orange and some others

 

my method (i know its kinda lame)

-swab teeth

-streak onto agar plate

-add 0.5 ml of essential oil to the centre of the agar plate

-incubate

-measure zone of inhibition

 

but my sister suggested this method :

-mix 2.5 ml saliva with 2.5 ml sterile water

-dip swab into this solution and streak agar plate

-using a straw, cut out a circular piece of the agar, forming a well

-using a dropper , fill the well to the top with essential oil

-incubate

-measure zone of inhibition

 

which method do you think is more accurate?

thanks

Edited June 19, 2011 by sonna10

[Genecks]

You need a control.

You'll be using the pour-plate method with agar.

You'll want to melt, slightly cool, inoculate, and then pour the agar into a plate.

 

Your sister's method sounds interesting. Try it.

Try both. It shouldn't take too much time.

Getting the pour-plate method right, however, can take effort.

[CharonY]

Ideally you should work with cultured bacteria rather than swabs. It is kind of tricky go get good lawn based on a swab, especially as you are going to have a very heterogeneous growth including fungi.

 

Also, streaking often does not result in a nice lawn, diluting the bacteria into soft agar and pour it tends to work better, or dilute them into media and use a spreader (not deionized water, as some bacteria are not osmotically stable enough to survive that). The well method is more accurate than using droplets. Alternatively, use a sterile piece of filter paper (with defined size) and soak it in the compound to be tested.

 

[sonna10]

thanks for replying

 

Genecks - I did two controls - one agar plate with olive oil (non-essential oil) and an empty agar plate. I didn't make my own agar because I'm pretty sure I would have contaminated it and its just too messy and annoying. i went with my sister's method.

 

CharonY - You were right. i didn't get a lawn, just single colonies, so i couldn't even measure the zone of inhibition .. experiment was a fail :'(

i used 'sterile water for injection' from my mom's clinic. is that deionized water? im not sure

plus there were fungal colonies on a couple of the agar plates

 

the only measurements i made were:

1. number of colonies (very inaccurate and not even related to my method .... i just assumed that the essential oil diffused through the air and inhibited bacterial growth in the whole of the agar plate ).

2. distance to the nearest colony (which is pretty inaccurate too because that just depends on chance , the colonies would grow where the bacteria was swabbed).

 

i did the well method that my sister told me to do. the filter paper idea seems really cool .. i dont know why i didnt think of that before.

 

but i dont know what to do now because my project is due in 2 weeks and i have to do all the results, analysis, graphs, discussion, and stuff ... do you think i will have time to do the experiment again? i dont have an incubator. so it will just be bacteria growing at room tempature. but the growth was pretty good at 3 days .

 

i attached some photos of my results... i did two people. one of them brushed their teeth just before the experiment so i dont' think their bacteria is oral bacteria. they were just recovering from a cold , so maybe its that, . its looks really yuck lol....

 

 

1. example of results for subject 1(i have no idea what bacteria this is- maybe cold / flu bacteria?)

best one: they were all pretty bad but i guess the tea tree oil

 

 

worst one: all of them

 

 

 

2. example of results for subject 2 (it looks like streptococcus mutans)

best one: peppermint

 

worst one: control

[Guest latex123]

good idea!