Identifying Unknown bacteria

Hughes Lee E lhughes at jove.acs.unt.edu
Sun Jul 24 23:41:14 EST 1994


suguitan at ucssun1.sdsu.edu (Norman Suguitan) writes:

>I am taking 
>a General Microbiology class in a community college and the class has started
>the identification of unknown bacteria.  Each of us was given a mixture
>of gram positive and gram negative bacteria.  I was able to isolate
>both bacteria and has grown a slant and broth.

Did you do a Gram stain of the original mixture?  What did you see then?

>When I looked at the gram positive bacteria under a microscope, the cell
>morphology was clearly coccus, and staphylo in arrangement.  I even asked
>some of my classmates to verify the shape and everybody agreed.  
>Then I performed some biochemical tests to determine the unknown gram
>positive.  Well, I got it wrong.  My teacher said it was a rod gram-positive.
>This was shocking, and almost unbelievable.  Did I and my classmates really
>see a cocci bacteria?  The bacteria didn't look rod at all.  If they were
>a rod, what could have caused the bacteria to look like a coccus?  Need help.

You could have been given a Gram positive rod in the original mixture, 
but actually isolated a Gram positive cocci (contaminant).  Did the 
instructor look at what you isolated?  S/he could confirm what you 
actually have now.  It might not help if it isn't the organism you were 
supposed to isolate, but at least you'll know if your identification of 
what you have is correct.

BTW, "Gram" is a person's name, so should be capitalized.

Lee
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