John Gentile yjgent at
Sat Mar 10 19:10:40 EST 2001

Be VERY, VERY careful when decolorizing your Gram stain. Look to see what
media it grows on. There are very few Gram Neg rods that do not grow on the
usual Gram neg agars like MacConkey's.

Don't assume that every microbiology test is a hard and fast rule - there is
a great deal of "gray" in between the black and white (or the Gram pos blue
and the Gram neg red). An accurate Gram stain is best done on a fresh
organism - try one from a 6 hour broth culture.

A case in point - you probably learned that E. coli is a lactose fermenting,
indole positive, motility positive GNR. I've seen E. coli colonies that were
non lactose fermenting, indole negative, motility negative and 1 that was
H2S positive - it looked like Salmonella.

John Gentile                                    Rhode Island Apple Group
yjgent at                                      President
"I never make mistakes, I only have unexpected learning opportunities"

From: Aimee023 at
Organization: BIOSCI/MRC Human Genome Mapping Project Resource Centre
Newsgroups: bionet.microbiology
Date: 10 Mar 2001 20:12:54 -0000
Subject: help!!


I'm a Bacteriology student working on an unknown experiment.  We were to
isolate 2 unknown organisms and determine their identity down to Genus and
Species. I have had no problem getting the 2 organisms isolated and growing
successfully.  Here is my problem....I did several Gram Stains on Organism B
and it is definitely Gram Negative, the rods are short but there are
endospores!!  I did 2 endospore tests and my TA also concluded that I had
endospore formation.  I didn't think Gram Negative bacteria could produce
endospores. My TA cannot give me any additional information because this is
an independent assignment.  There is a list of possible organisms and my
unknown B doesn't fit any of these.  Can anyone provide
suggestions/advice...I would greatly appreciate it =)

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