E. coli sheen on EMB agar

fintan_v at Msu.oscs.montana.edu fintan_v at Msu.oscs.montana.edu
Wed Feb 8 18:37:47 EST 1995


In article <95020716404674 at picard.colsf.edu>, stuhansenmic at PICARD.COLSF.EDU writes:
>I am an undergraduate biology major that recently finished an intro to 
>microbiology class.  An organism isolated appears to be E. coli, according to
>IMViC results, several sugar fermentation tests, and a Biolog microtiter
>plate, but it won't produce the characteristic green metallic sheen on EMB.
>Can anyone tell me if this is common? I have found no real answers in any
>books, including Bergey's and The Prokaryotes.  Also, what causes the sheen
>to form in the colonies?
>
>Thanks in advance for any help.
>
>Mike Hansen
>                      

The metallic sheen is due to the large amounts of acid the E.coli produces
on the EMB agar. The acid causes an amide bond to form between the two dyes
(eosin and methylene blue), giving rise to a sheen.

The sheen is only visible where you have alot of organisms growing
close together. Typically it is not visible on single colonies. If you
want to check streak over the entire surface of the plate and see what
happens. 

Fintan




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