Goshko, M.A. "The Use of TTC in USP Plate Count Medium For Enumerating Low Levels of Bacteria From Insoluble Materials"

I believe this article is from Pharmaceutical Technology Magazine during the 1980's.

TTC (2,3,5-Triphenyltetrazolium chloride) is a redox indicator which when acted upon by microorganisms, forms the insoluble red pigment formazan.  The reaction is irreversible.  I have TTC in Motility Test Medium in the past with good results.  

TTC 1% is available from BBL in 20 mL/tube.  The catalog # is 12237.  

Robert R. Friedel
Quality Assurance Manager
Laboratory Research & Analysis Groups
Perritt Laboratories, Inc.
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  ----- Original Message ----- 
  From: Laura Acevedo 
  To: [log in to unmask] 
  Sent: Thursday, October 14, 1999 6:32 PM
  Subject: [PMFLIST] Inhibitory effect of TTC.

  Dear colleagues,
  I perform microbial limit tests using poured plates . With some products (lactose, starch) it is difficult to distinguish the colonies. I know there`s the recomedation of using MPN in this cases, but I wonder if it is possible to use poured plates adding  TTC to the culture medium to stain the colonies and differentiate them from the product being tested. Has anybody validated this method? I`ve heard about possible inhibitory effect of TTC. Could someone refer me any paper on this topic? 
  Any help would be appreciated, thanks in advance,
  Laura Acevedo
  Microbiological Quality Control Manager
  Laboratorio LIBRA
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