Microbiology Unknown Bacteria

[hep1487]

I am in a summer microbiology class that only meets once a week. We were given a random unknown bacteria and have to figure it out. The possibilities for this random bacteria are

1. Eschericia coli2. Enterobacter aerogenes

 

3. Staphylococcus epidermis

 

4. Streptococcus salivarius

 

5. Clostridium sporogenes

 

6. Serratia marcescans

 

7. Kocuria rosea

 

8. Klebsiella pneumoniae

 

9. Mycobacterium smegmatis

 

10. Proteus mirabilis

 

11. Proteus vulgaris

 

12. Sarcina lutea

 

13. Pseudomonas aeruginosa

 

14. Lactobacillus acidophilus

 

After doing a Gram stain and observing it under the microscope I discovered my unknown bacteria is Gram positive and bacilli. Knowing this narrowed my possibilities down to Clostridium Sporogenes, Mycobacterium Smegmatis and Lactobacillus Acidophilus. I then learned Mycobacterium Smegmatis does not stain well with Gram stain (correct?) so I removed this from my possibilities as well. My teacher gave us different tests to do depending on if the bacteria was Gram negative or positive. The tests I did on my bacteria were PRL (phenol red lactose),PRS (phenol red sucrose), PRD(phenol red dextrose), citrate broth, MSA (mannitol salt agar), and EMB. I was supposed to do TSI but some things were unlabeled and accidentally did EMB instead of TSI so that result is pretty irrelevant. My results:

 

PRL- negative

 

PRS- negative

 

PRD- positive

 

citrate- positive

 

MSA- growth but no color change (halophile)

 

I thought both possible bacteria would ferment lactose, sucrose and dextrose so this may be a mistake and I may redo my tests but my teacher says I do not need to and I should be able to figure it out.

 

I also think Lactobacillus Acidophilus would not have a positive result in the citrate broth so that leads me to believe my bacteria is Clostridium Sporogenes but why wouldn't it ferment the lactose and sucrose?

 

 

[JorgeLobo]

None of those tests was esp helpful for your suggested bacteria. If these were the options, simple culture and microscopic examination would have been sufficient. In fact, it's neither of these. You really need to read Bergey's descriptions but even wikipedia would have provided enough info to rule out both. Redo your Gram stain with pos and neg controls., then read Bergey's descriptions of the possiblities and select tests based on a rationale.

[Marcus Williams]

Can anyone tell me what the best use of LB broth is? I think I heard it was used for bacterial transformation, but i am not entirely certain! I know this is kind of unrelated, but i was just searching anywhere for an answer.

[ecoli]

Can anyone tell me what the best use of LB broth is? I think I heard it was used for bacterial transformation, but i am not entirely certain! I know this is kind of unrelated, but i was just searching anywhere for an answer.

LB is used to culture many different microorganisms for a variety of purposes: http://en.wikipedia.org/wiki/Lysogeny_broth

[Marcus Williams]

LB is used to culture many different microorganisms for a variety of purposes: http://en.wikipedia..../Lysogeny_broth

 

 

Thank you very much for the info!