Wednesday, July 16, 2008
Good News, Mr. Yen-- It's An E. Coli!
Last week, my lab partners and I ran various tests on both gram negative and gram positive bacteria and recorded the results. Last week we were each issued an unknown bacteria sample and we had to first figure out whether the bacteria was gram negative or positive, and then run the appropriate tests.
After determining last week, through gram staining, that I had a bacillus-shaped (rice-shaped) gram negative bacteria, I ran the gram negative tests on it.
As I ran the tests, I expressed the hope that my unknown was E. Coli, mainly because E. Coli has a unique result in the Easion Methylene Blue (EMB) test; the culture turns a really cool metallic green.
As you can see from the picture, I got my wish. When I took my cultures out of the incubator this morning, my EMB test was metallic green, indicating the likelihood that my unknown bacteria, whose current name is "Unknown #24," is E. Coli. This conclusion was bolstered by the fact that it also turned the McConkey agar dark pink, indicating a lowering of pH caused by the fermentation of lactose.
My Triple Sugar Iron (TSI) "stab and streak" test, which is a differential test-- it tests for multiple things-- mostly backed up my E. coli conclusion. The slant was yellow, indicating that the bacteria metabolized lactose and/or sucrose, which is consistent with E. Coli. The "butt" was not black, indicating no hydrogen sulfide production, again consistent with E. coli. and there were bubbles in the "stab" portion, indicating carbon dioxide production, again a sign that Unknown #24 is E. coli.
The only inconsistent finding was that the "butt" portion, the bottom of the test tube, was red, rather than yellow. If it is E. coli, it should ferment the glucose in that portion of the test tube and turn the agar yellow due to a change in pH. My professor said not to worry-- give it an extra day; it sometimes takes an extra day for that to turn.
Man, I love this stuff!