for enumeration and differentiation of enteric pathogens in urinary tract infections.
CHROMOGENIC UTI AGAR, MODIFIED is used for enumeration and differentiation of enteric pathogens in urinary infections. The medium contains Peptic digest of animal tissue and Beef extract are the sources of nitrogenous compounds and essential vitamins. Casein enzymatic hydrolysate is a source of carbon. Chromogenic UTI agar contains two specific chromogenic substrates which are cleaved by enzymes produced by Entercoccus spp., Escherichia coli and coliforms which facilitates and expedites the identification on the basis of different contrasted colony colours produced by reaction of specific enzymes. Presence of rich source of phenylalanine and tryptophan from peptone and tryptone provides an indication of tryptophan deaminase activity, revealed with TDA reagent (TS 208) indicating the presence of Proteus species, Morganella species and Providencia species which appear brown. One chromogenic substrate is cleaved by β-glucosidase possessed by Enterococci resulting in formation of blue colonies. Escherichia coli produce pink-red colonies due to the enzyme β-D-galactosidase which cleaves the other chromogenic substrate. Further confirmation of Escherichia coli can be done by performing indole test using DMACA Reagent. Also some strains of Enterobacter cloacae lacking β-glucosidase show pink colonies indistinguishable from Escherichia coli. The DMACA Reagent (TS 207) for indole test (should be performed on filter paper) distinguishes between Escherichia coli and Enterobacter. Escherichia coli produce colonies that are rose to magenta in colour, with darker pink centers. No further testing is needed. Enterococcus spp. appear as small, teal to turquoise coloured colonies. No further testing is needed. Staphylococcus aureus produce opaque, golden yellow colonies. Note: Colonies may turn pink after 72 hours. Further biochemical tests are needed for complete identification.