Any Hints for Microbiology "Unknown"?


We are starting our "unknown" lab this week and we each will get 2 types of bacteria that we need to identify on our own. I plan on doing a gram stain for each, then do streak plates w/selective media.

Does anyone have any hints? I did find a website that you can put info into it and it will narrow it down, but if anyone has a site that could help?

Thanks in advance for your help!



32 Posts

Is your T.A. or professor not guiding you through the experiments? Ours did and here are the tests we were required to do:

Gram + Unknown:

Gram Stain

Streak Plates on:





& Blood Agar.

I was able to determine my unknown mainly from the MSA agar and Blood Agar. I had a strong Beta on the BA and a completely yellow plate n the MSA agar.

For Gram - Unknown, we did:

Carbohydrate Broth tests (although prof said this was most unreliable of the bunch)

TSI Agar

EMB Agar

Citrate Agar

Urea Agar

and Hektoen Agar.

We were given a chart with all these Agars and also a flowchart where we were to record the results. This really helped visualize all the tests done and to confirm a result. I hope this helps, and good luck!


58 Posts

Specializes in OR Pre-op, Post-op. Has 1 years experience.

we had a flow chart also. once the gram stain was done and the shape visualized we just followed the flow chart and inoculated the appropriate media. i was worried at first but it was pretty simple. they didn't give us anything we had not already seen and practiced on


144 Posts

I have no help to offer but I am also doing my unknown now. I would love that web site that helps narrow it down. I think I have mine down to one but I am not certain. Thanks. Colleen


37 Posts

Hi - I just wrapped up my second unknown for the semester in Micro. Our entire class knew we had Gr - enterobacteria, but we did about a dozen different tests to narrow it down. One of the big ones was the motility test, are you doing that one? Either with nitrate or a hanging drop slide. Also, does your instructor have copies of Bergey's manual that you can use? Our lab manual had several flow charts that helped too.

Good luck!


128 Posts

Specializes in Psych, Tele. Has 1 years experience.

We just turned in our write-ups and lab journals for our unknowns. Our class was fortunate enough to have a lenient professor who gave us a flow chart, and help when needed. A friend in my A&PII class said they got their unknowns and were on their own from there on out.

I had pseudomonas aeruginosa, and staphlococcus xylosis. Both were easy to identify due to their color change on the media. Pseudo turned a mossy green color, and staph turned the TSA blue yellow.

The changes in the media alone made it possible to determine what my unknowns were.


196 Posts

Several tests will need to be conducted as I'm sure you probably have already completed.

Here's the tests we needed to do

Gram stain

Tests which determine the organisms oxgen requirements {facultative anaerobe, aerobe, anaerobe etc.}

Oxidation and fermentative tests {Oxidase, MRVP, catalase, we probably did about tests concerning this area}

Fat Hydrolysis

Starch Hydrolysis

Casein Hydrolysis

Citrate {to determine carbon source}




it went on and on there were probably about 10 more I didn't name... I'm just guessing off the top of my head as we did the experiment back in early March and I don't have my research notebook with me. Once completed, we used the API-20E test to conduct a series of what I call confirmation tests and based on the results we were able to determine a 6-8 digit # like 2 00 126 that we used to look in this book (reference book with about 100,000 organisms) like most of the numbers did not add up because one test may have been inconsistent with the conclusions etc. May have interpreted test results properly...

Then we went to the flowchart which there were several. Based on the organisms o2 requirements, motility, urease test, indole, H2S ability to ferment glucose or lactose etc we were able to narrow it down to possibly 1-2 organisms. We had 2 chances to give the right name for the organism but both answers had to be given at the same time. Lots of pressure here because if we guessed it right... we got the points for the lab:D if not no credit was given:(.

We had 3 days to come to a final decision and everyone had a different organism. NO TA help. Not because they were being jerks but because they required us to perform all of those tests for a reason so that we could independently come up with a conclusion without guided assistance. My organism, I'll never forget it was :redpinkheProvidencia Stuartii:redpinkhe


9 Posts

Thanks a lot for the websites, they are very helpful!

As for this, we only have lab 1 day a week, we only have 3 weeks to do it. We have to streak plate, and do all the other tests that have to be incubated, tonight-it's a 3 hour lab. Next week we have to have it narrowed down, so we can finish the next week.

We don't have flow charts, we only have a computer program, to use when narrowed down to 2 organisms, it will say if we did the right tests.

As for our instructor, he's pretty good so I am asuming he will guide us a little, but there are 25 in the class.

Wish me luck.

This topic is now closed to further replies.