unknown in microbiology

GrnHonu99, RN · Jun 27, 2005

Hi
i have next week the unknown lab, please what to expect? i am doing well on lecture exams however lab is giving me some difficulties.
i would appreciate any information or input regarding the unknown test: what to expect?
thank you.

my unknown was done in lab. My teacher gave us a vial in which we expected to prepare a gram stain...after that we were expected to perform all the different tests we had learned in the quarter to help identifiy what two organisms were in our vial...lets see...I made my gram stain and looked at it under the scope...i also grew my organisms on the diff agar plates...if it turns the manitol salt agar yellow and there is growth then it is staph aureus, i think...lol...then there is the test that you do on the blood agar...and so on...oh and the test that you use the hydrogen peroxide and see if it bubbles...etc..we had a chart that listed a bunch of diff. organisms and we could compare the results of our test and see what organism it matched up to on the chart...oh and make sure you note the hemolysis of your organisms on the agar...

the tricky thing with mine was that since the organisms we had in lab had been grown so many times and recultured that when i grew them on the blood agar they came out gamma hemolytic even though they were supposed to be beta..my instructor chalked it up to them being grown and regrown so many diff times...threw me off!!!

I think I ended up with staph aureus and ummm..cant remember lol

Fun2, BSN, RN · Jun 27, 2005

We are doing our unknown now.

We were given a inoculated nurtrient broth in which we checked the growth, noting surface, subsurface and sediment. Then we Gram stained to check for purity, noting G+ or G-, and the arrangement (tetrad, diplo, chains.....rods or cocci). If ok, then we inoculated a nutrient agar plate. 24 hours later we examined the colonies, noting colony size, margin, configuration & elevation. Then from 2 different colonies, we inoculated 2 nutrient agar slants. One was incubated at 37 degrees, one at 25 degrees.

24 hours later we noted the growth on the agar slants for opacity, pigment, and form. Next, we had to gram stain from each tube to make sure these stocks are pure. If so, the best growth was marked as the reserve stock, and the other became our working stock. The optimum temperature is noted.

All future test are performed using the working stock. The reserve stock is refrigerated and only used to make a new working stock. (If a new one is made & incubated, it must be re-gram stained.)

Tests that run include many sugar tests: glucose, sucrose, lactose, mannose, manitol, galactose, and other tests such as nitrite reduction, Hydrogen sulfide production, phenylalanase, oxidase, indole. MR-VP, citrite utilization. urease etc

I had gram positive cocci, and the catalase test was ran as the last test on my working stock. It was positive greatly narrowing down some of the possibilites.

Since I have already made a new working stock, all future test will come from that.

In fact, I have to go in today because I went in Saturday and inoculated about 7 tests.

Keep great records of what you do everyday in a spiral notebook. That will help you. Your instructor will probably give you a descriptive chart to where your results should be noted. If not, let me know. I'll e-mail you a copy of what we were given. It helps to see all the results in one place.

Also, make sure to do the 30 day tests first....urease, gelatin liquefaction, etc, and make sure to pay attention to incubation times. For example, don't do a 24 hour test on the last class day for the week.

After gathering all you results, and figuring the best possibility, you turn in your guess in whatever manner required by your instructor.

Good luck.