Fall 2015 Week 7

Some of the literature about endophytes I've read in the past have said more diversity can be found if plant metabolites are on the petri plates. So a few weeks ago I ran an experiment where I blended up some S. eleaegnifolium leaves, strained the slurry and poured the liquid on petri plates filled with PDA, rose bengal dye and streptomycin to see if I could grow anything other than the usual fungi.

Unfortunately I forgot to surface sterilize the leaves I blended up but I did grow something really interesting. On my plates were small, rounded, sticky looking, creamy white colonies that could have been either bacteria or yeast. I isolated it to a few different media but it only grew well on the TSA plate. Here's what it looked like after a few days: 

But it's way cooler now: 

I did a gram stain and found out the organism is a gram positive bacillus bacterium. This is especially interesting because the streptomycin on the plates I make is supposedly broad spectrum enough to kill most bacteria. The plates were made in April so maybe the antibiotics degrade, I thought. I made a streak plate of 4 different bacteria species I knew to be susceptible to streptomycin on one of the last plates and nothing grew. I assumed both that my antibiotics were working and the bacterium was immune to streptomycin. Then I did an antibiotic test plate with four different antibiotic disks: Streptomycin, vancomycin, penicillin and chloraphenicol. Here's what I found:

Everything except penicillin has a zone of inhibition. WHAT? Not what I expected. The concentration of the antibiotic disk was 10 micrograms, about what the concentration in the agar should have been. I looked back in my notebook and guess what? I diluted my streptomycin to about 1/10 of the strength I thought it was. Decimals are hard to keep track of. So now I know those plates were not exactly what I thought but they did their job well enough while I used them. Interesting.