On 17 May 1995 Enevold.Falsen at alinks.se wrote:
> ---------------------------- Forwarded with Changes ---------------------------
> From: MIME {ccugef at ccug.gu.se} at UUCP
> Date: 5/16/95 4:27PM
> To: Enevold Falsen
> *cc: - {uh at sik.se} at UUCP
> Subject: Tetrazolium chloride
> -------------------------------------------------------------------------------
>> >From: "Ulrika Husmark" <UH at sik.se>
> >To: Falsen at ccug.gu.se> >Date: Tue, 16 May 1995 13:48:55 GMT+0100
> >Subject: Tetrazolium chloride
> >Reply-To: Ulrika.Husmark at sik.se>> >Does anyone know if there are some bacterial species that does not
> >form red colonies when grown on medium containing tetrazolium
> >chloride?
> >
>
The formation of the red colonies by some bacteria is due to reduction of
TTC to insoluble red Formazon. Increasing the acidity around the colony
prevents this reduction and causes the colonies to appear as white.
This, to some extent, depends on the concentration of the TTC. Using some
particular compounds in the medium and in presence of TTC would raise
white colonies. For instance, in enumerating Lactococcus lactis
sub-sp lactis and Lactococcus lactis sub-sp cremoris one potential way to
differentiate them is to incorporate Arginine into the medium.
Lact.lactis is able to produce ammonia from arginine while lact.cremoris
not. In the first stage of incubation both bacteria will appear as white
but latter, liberation of ammonia by Lact.lactis would result in red
colonies. The adjustment of the pH is critical.
Hamid Ghoddusi
