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Need help Identifying Unknown Bacteria...

Need help Identifying Unknown Bacteria... - Microbiology Forum

Need help Identifying Unknown Bacteria... - Discuss Microbiology Science and Protocols here. Post questions on the study of viruses, fungi, parasites and bacteria here. Microbiology Forum.


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  #1  
Old 07-31-2011, 02:29 PM
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Default Need help Identifying Unknown Bacteria...



I'm new here and apologize if this is in the wrong section. If a mod could redirect it to another section that would be greatly appreciated.

So I'm in microbiology class and our last project we need to do is identify an unknown bacteria.

We inoculated 3 plates a Nutritional Agar plate, Blood Agar, and endo Agar.

The morphology was convex, more circular(mucoid on the blood agar), even margins, and a whitish/clear color.

In the nutrient broth, in a test tube, there was sediment, turbidity, the color was a yellowish/white, and was unsure of the pellicle. I thought there wasn't but I'm going to check again.

When I took a gram stain I found the following:

Cocci in clusters
Spores -
Motility +
Gram -
Acid fast -

The Biochemical results I got were:

Catalase +
Indole -
Methyl Red -
Voges-Proskauer -
Hydrogen Sulfide-
Nitrate Reduction +
In Phenol Red Glucose it produced an Acid and a gas
Phenol Red Sucrose Acid and gas
Phenol Red Lactose it was a slight dark orange- so I put negative

In the plates-
Endo agar- there was a lot of growth and a pinkish color, so that would further confirm that it's gram negative and the reddish color should make it Lactose positive. So there's conflicting results right there

Blood agar- A lot of growth as well, I believe it was Beta hemolytic.

Mannitol Salt tube- There was growth, but it was clear. Not yellow, so it couldn't ferment the mannitol

The Triple Sugar Iron tube showed A red slant and yellow on the bottom
Growth +
Gas production +
Multiple sugar fermentation - (Only showed glucose)
Hydrogen Sulfide - (No black)

Litmus MilkWas unsure of this, it was white in the whole test tube except for like half an inch space at the top where it was a purple color, similar what it original looks like)

Acid ?
Alkaline ?
Hard curd -
Soft curd ? I think it may have been a rennet curd
Reduction + due to the white color
Peptonization -

So this is where I'm completely lost. He has a list of bacteria that it could be and makes it a little easier by giving us a growth temperature, so we can easily divide them. Mine was between 25-30 degrees Celsius.

The only two that I could think of that are anywhere near my results would be either:

Neisseria subflava
Enterobacter aerogenes

The only conflicts i have with N. subflava is that it is Hydrogen sulfate postive, and I did 2 tests that show it is negative. I know it's capable of fermenting sucrose and glucose, but am unsure if it can make gas from it.

The conflict I have with E. aerogenes is that it is capable of fermenting Mannitol salt and it tests positive for the VP test. Also, it's more rod shaped than cocci so I am unsure of that. Also E. aerogenes is a slow fermenter of lactose, so that could explain the results of the Endo agar and the Phenol red results.

The only other thing I could think of is that my results were somehow contaminated because two people next to me weren't doing the correct aspetic technique. When they were inoculating their tubes, the wouldn't wait for their inoculating loop to dry all the way and just going right in the tube so it would make a hiss sound. So that could have created an aerosol and their bacteria could have gotten into my testing tubes.

I really need some help on this because I'm completely lost. Thanks for your time.

Last edited by admin; 07-31-2011 at 02:58 PM.
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Old 08-03-2011, 09:17 PM
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Default Re: Need help Identifying Unknown Bacteria...

it is enterobacter.
neisseria would not grow on endo agar.
Is the colony adherent to the blood agar ? Neisseria is.
I really didnt look thru all your test results but I would bet its your gram neg. bacilli your working with.
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Old 01-20-2012, 03:15 AM
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Default Re: Need help Identifying Unknown Bacteria...

Enterobacter aerogenes are gram negative rods.
Neisseria on the other hand are gram negative cocci.

I think the fact that they are gram negative cocci should have helped differentiate them.
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