microbiology unknown help! I am so frustrated.

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I am running into some frustrations with my unknown. This is a summer class, so we only have this week to work on the unknown. The only info we are given is 16 possibilities (which we had to track down the test results for over the semester) and the tests we must run to gain some of our points (if they give the correct result).

I did my gram stain yesterday and at first I thought I lucked out because it automatically narrowed it to three possibilities. Gram positive cocci in pairs or short chains and the only three that meet that description are E. faecalis, S. salivarius and L. lactis. So then I started double checking all of my info on those specific microbes so I could be ready to identify during our next (and last) lab and I'm finding that every single test we are using has the same result for those three. We are NOT using any tests that would actually ID between those three. We are doing motility, catalase, glucose (and gas), lactose (and gas), TSI, citrate, MacConkey's, thioglycollate, indole, gelatinase and then she will give us the oxidase test results since we don't have the test materials. No blood agar, no mannitol salt agar, no other hydrolysis tests that would indicate between Streptococcus, Lactococcus and Enterococcus.

I am feeling frustrated and like I must be missing something. I've worked really hard to fill out the charts with these test results. I rented Bergey's (what she recommended using), so I could use that at home (two kids = no library time), I've searched all over online trying to use reputable sources and I still cannot find anything! So my thought is 1. I'm missing something and am going to totally screw up my unknown and that makes me mad because I've worked so hard, 2. maybe I should redo my gram stain Wednesday IF I have time just to double check OR 3. MAYBE the answer is that we cannot ID between those three because all of the tests we are using are better for gram- rod ID, specifically Enterobacteriaceae - something that has shown up time and time again as we've practiced the tests throughout the semester.

Any help?? What should I do? :( We can use any source imaginable at this point (including discussing with others and classmates) outside of asking the professor at this point.

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Ii just finished this class last week. I also had that same problem with 3 possibles. Look at your thioglycollate test and make sure that matches, optimal growth temp, oxidase and citrate. I was pretty frustrated also. What I did was chose 1, put habitat for all three, and gave a rational of further testing that could be done to narrow down the possibles to one. I ended up getting full credit. If u have time like you said double check your gram stain, that is the most important test. Then pick one with testing rational if u have more than 1 still. Good luck and hope it all comes out good. P.S also the 4 streak method helped with color of colonies as well as the smell of the cultivated bacteria, for example e-coli has a very distinct smell compared to some of the others, not sure of the smell of your bacteria tho, just a suggestion. Also mentally see which tests could be variables and cultivation wasn't long enough. Some of the IMViC test could be variables that required longer cultivation that wasn't practical in a summer course.

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Specializes in Cardiac Stepdown, PCU.

I didn't have to do this for my Micro class, but if I were in your place, I would have just asked my professor what we were to do in order to ID the unknown if the tests cannot differentiate the microbe. You don't have to ask her how specifically, just ask her if your supposed to be able to. If she says yes, then you did something wrong, or something is missing. Its likely something very simple that you overlooked.

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Specializes in ICU.

I'm trying to remember the difference between strepto and ecoli. I thought Ecoli strains were bacilli. We did all of our testing on the computer and I had a problem with my indole test. But mine were bacilli and I thought ecoli was one of my choices. I know there are many strains of ecoli I just thought that was one of the characteristics. I would double check everything because you shouldn't have 3 choices with no test to differentiate. We were not allowed to ask our professor any questions. Mine was obvious, I just misread the indole test.

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E. coli is Escherichia, which is a g- rod. Enterococcus is something else a g+ Cocci. It used to be classified with Strep, as did Lactococcus.

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E. coli was used just as an example for different smells between bacterias, I agree with OP I would pick the instructors brain some on this,or other students that have the same three possibilities as you. Your three choices I believe are all faculative anaerobes, optimal growth temp approx 37c.?. Not sure how they responded to carbohydrate testing, I am sure you have gone over this many times on the flow sheet paper and are getting more discouraged by the minute. I would talk to the instructor for sure. Sorry can't be more help without being able to do the tests myself to see if there are possible variables.

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Thanks, everyone. I'm going to see what my test results are tomorrow, probably redo my gram stain and see who else has my results (if anyone) and go from there. If I don't get any further, I'll ask if it's a possibility to actually not be able to ID from these tests alone and see if she gives me an indication. She was pretty clear that she would not give us any help whatsoever after we were handed our unknowns. :-/

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If my info is correct (and I mostly got it all from Bergey's), all there are nonmtile, catalse negative, oxidase negative, ferment glucose and lactose, but do not produce gas, do not produce H2S on the TSI test, will not grow on MacConkey's (gram positive), indole negative and gelatinase negative. Citrate and TSI are the only two tests I had some difficulty in tracking down (I'll look again tomorrow in the books she has in class), but she also that if we absolutely could not find a specific result (or it was variable), we were not to use it for IDing the unknown because it probably wouldn't help anyway.

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sorry! Our unknowns were the most frustrating....I am fairly certain our samples got mixed up (there were 3 of us in my lab that answered the same on one of our unknowns...we had 2....and got it wrong when it should have been something else). I had a night lab and it wasn't uncommon for our samples to sit out all day....or not be very organized once the other labs have finished. and our professor would NOT help with the unknowns...at all....luckily because of our testing rationale we still got an A on the unknowns but frustrating that we didn't get full credit when it was likely a mix up in the samples :(

ANYWAY sorry you are having trouble...hope you figure it out!! I would double check all your results and then give the rationale for additional testing that could further identify. as suggested by someone else

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The unknown can be stressful. When I did mine I found out that the sample was contaminated so all the results were skewed. My professor told me that in all honesty, it is almost impossible to correctly identify an unknown using the tests given so I wouldn't freak out at this and when you are finished will all of your tests compare all of your data and make an educated guess. Most importantly, make sure you clearly write your issues in narrowing down the unknown and your analysis in your lab report and most likely the professor will give you full credit.

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Thanks everyone. I did redo my gram stain and my original hunch of misidentifying the shape was correct, though I had the professor confirm it. I ended up having B. subtilis, though I incorrectly ID it as a couple others before that. She would let us have her "check" our results before officially turning in the work and then would redirect and guide us short of actually giving the answer, which I appreciated. It was super frustrating for me, though. I did write out my thought process and mistakes in IDing and I got some other key points right without help (my streak plate was great and most of my tests have the expected result). I just found it very frustrating that we're supposed to determine an unknown correctly by matching stuff that may actually be variable! How do you know what to focus on unless you actually do this a lot. :-/

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Good glad it all worked out, when I did mine I had a coccusbacilli mix, some spheres and some rods. Was a real pain, but thankfully it is over!

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