Trying to grow bacteria on skin for a study - (Nov/29/2013 )

Hey folks, 

I'm new here, and actually the problem this thread is about is the reason I registered here. 

So, I'm doing my internship in a dermatology lab and what we're trying to do is grow bacteria on pieces of skin. 

It's a very early phase of a study about the skin-microbiome (the complement of commensal micro-organisms that populate the upper layer of the skin). 

Before we can do any further research we first need a way of growing bacteria on pieces of human stomach skin and then harvesting these bacteria to compare the resulting CFU counts and thus amounts of cells with the amounts of cells we infected the skin with before letting it grow in the incubator. 

Now the problem is: we've tried growing three bacteria on these pieces of skin (and also in little artificial punctures we made in the skin), we're using: S. aureus (pathogenic), S. epidermidis (commensal), P. acnes (commensal) and you would expect that after you put the infected skin in the incubator, let it grow overnight, plate it out in a dilution series, and count the CFU that you would end up with a higher amount of bacteria on the infected spots on the skin than in the original sample that you infect the skin with. 

And that's the problem: our bacteria don't grow, they die. We've tried growing in a normal incubator at 37 degrees Celcius (with and without a glass of water next to the petri dish with the skin in it, to raise the humidity), we've tried growing it in a CO2 incubator. To no avail. In our BEST grown sample, still: we only end up with 0.45% of the original bacteria. Which is the opposite of what we want.

Do any of you have any suggestions regarding how to make these bacteria grow on skin? Which is what they're supposed to do right, not have 99.5% die off. . 

Best,

Sam 

Culture-based studies of skin bacteria have always been pretty imprecise and skin inoculation studies and such ex vivo studies have very limited significance.   That's why you'll see so few culture-based studies published in the last decades in this context.  You might review the older studies of Kligman and Leyden.

Can you explain to what natural phenomena you see this as a valid approach?