Help re:"Coning" Phenomenon Within Agar Inhibition Zone Edges

David E. Post david.post at virgin.net
Sat Feb 17 15:15:19 EST 2001

Assuming you are referring to disc diffusion testing might this not be an
effect of a diffusion gradient which is maximum at the surface and decreases
with increasing depth?   David Post
Stephen W Mamber wrote in message <3A8DA3FA.471A9384 at bms.com>...
>Can anyone give me some literature references, or perhaps a
>remedy, with respect to a phenomenon I refer to as "coning"?  My
>description of the phenomenon is as follows:  Certain antibiotics
>yield a sharp zone edge with a given organism, but within the
>zone, growth (partial growth) seems to increase as it extends
>into the agar.  It appears to be like looking down at an ice
>cream cone with the bottom cut off (which would be the area of
>complete inhibition).  My explanation for this is that decreased
>oxygen content makes the organism less sensitive to the compound,
>on the assumption that there is more exposure to oxygen at the
>surface of the agar than at the bottom.  I'm sure others have
>seen this, so any help regarding this phenomenon would be greatly
>Thank you,
>Stephen Mamber, Ph.D
>Bristol-Myers Squibb

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