Phenol Red Tartrate Agar

Principle And Interpretation

Phenol Red Tartrate Agar was originally formulated by Brown et al (1) and further modified by Jordon and Harmon (2), for the differentiation of Enterobacteriaceae especially Salmonella species. This medium can also be used to differentiate V. parahaemolyticus (positive) from Aeromonas species (negative) (3). Phenol Red Tartrate Agar with the addition of sodium chloride (25.0 g/l) can be used to differentiate halophilic Vibrio species e.g. V. parahaemolyticus, V. vulnificus, V. aglinolyticus and V. metschnikovii. On this medium, an acidic reaction is produced by Salmonella Enteritidis, Salmonella Choleraesuis, Salmonella Typhi, Salmonella Typhimurium, Escherichia coli and Proteus vulgaris. However organisms like Salmonella Paratyphi A and Salmonella Schottmuelleri produce an alkaline reaction due to non-utilization of tartrate.

Peptic digest of animal tissue in the medium provide the essential growth nutrients like nitrogenous compounds to the organisms. Sodium potassium tartrate is used most frequently because it is easy to be utilized by the organism. Tartrate utilization (fermentation) yields an acidic reaction, which is indicated by the yellow colour formation at the bottom of the tube. Phenol red acts as the pH indicator while sodium chloride maintains the osmotic balance of the medium.

Inoculum should be taken from a liquid or broth suspension (3).