Science Buddies: "Ask an Expert"

Hi I have a few questions regarding the project.
Would it be better if I use the staphylococcus epidermidis bacteria instead of e coli as staphylococcus epidermidis is gram positive bacteria similar to p. acnes? Since I heard that benzoyl peroxide has no inhibition zone in e coli.
Also I ordered the agar slant culture, would it better for me to inoculate it to broth first or just inoculate it to the prepared nutrient agar plates?
Do you think its okay to include all 6 acne medications into one agar plates?
Do I need to dilute the acne medications? I have benzoyl peroxide gel, tea tree oil, salicylic acid face wash, coconut oil, and triclosan face wash.
Also is it okay to use the nutrient agars that have been in the fridge for 1 week?

midkxo wrote:Hi I have a few questions regarding the project.
Would it be better if I use the staphylococcus epidermidis bacteria instead of e coli as staphylococcus epidermidis is gram positive bacteria similar to p. acnes? Since I heard that benzoyl peroxide has no inhibition zone in e coli.
Also I ordered the agar slant culture, would it better for me to inoculate it to broth first or just inoculate it to the prepared nutrient agar plates?
Do you think its okay to include all 6 acne medications into one agar plates?
Do I need to dilute the acne medications? I have benzoyl peroxide gel, tea tree oil, salicylic acid face wash, coconut oil, and triclosan face wash.
Also is it okay to use the nutrient agars that have been in the fridge for 1 week?

Hi midkxo,

It would be fine to use S.epidermidis over E.coli in this experiment to model the p.acnes bacteria as much as possible. Like most bacteria, however, please use S.epidermidis cultures with caution, as they can become pathogenic! (Additionally, S.epidermidis would be a better choice if an inhibition zone wasn't produced for some standard medication with E.coli)
For dividing the medications into agar plates, I would recommend dividing them up into separate agar plates (perhaps 3 on each plate, using 2 plates?); this gives the bacteria more room and will most likely give you better,more observable results (6 crammed into one agar plate gives very little room for inhibition zones to form as well).
Edit: The materials specify how many plates need to be used depending on the number of medications to be tested, so I would follow the chart within the Materials section!
For inoculating agar slant culture, either method is fine; however, speaking from previous lab experience, I have always inoculated with broth first before streaking onto plates.
The procedures don't specify dilution, so I believe that the concentrations of each of the medications will be fine.
Generally, nutrient agar plates should be used within the week they are made for best results; however, if you don't have time to make new plates, and if upon observation you don't find evidence of dehydration and/or colonies forming, I believe that they are okay to use.

Hope this helped,

JSK