Rapid UTI Diagnostic Slants

Principle And Interpretation

HiCrome™ UTI Agar, Modified is formulated on the basis of work carried out by Pezzlo (1), Wilkie et al (2), Friedman et al (3), Murray et al (4), Soriano and Ponte (5) and Merlino et al (6). These media is the modification of HiCrome™™ UTI Agar (M1353), which can be used in place of MacConkey Agar for isolation and confirmation of various microorganisms. It facilitates and expedites the identification of some gram-negative bacteria and some gram-positive bacteria on the basis of different contrasted colony colours produced by reactions of genus or species specific enzymes with two chromogenic substrates.

Enzymes produced by Enterococcus species, Escherichia coli and coliforms cleave the chromogenic substrates incorporated in the medium. Presence of rich source of phenylalanine and tryptophan from peptone and tryptone provides an indication of tryptophan deaminase activity, revealed with TDA Reagent (R036) 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. E.coli produce purple-magenta colonies due to the enzyme β-D-galactosidase which cleaves the other chromogenic substrate. Further confirmation of E.coli can be done by performing indole test using DMACA Reagent (R035). Also, some strains of Enterobacter cloacae lacking β-glucosidase show pink-colonies indistinguishable from E.coli. The DMACA reagent for indole test (should be performed on filter paper) distinguishes between E.coli and Enterobacter, and also between Proteus mirabilis and other species. Coliforms produce purple coloured colonies due to cleavage of both the chromogenic substrates Peptone, HM Peptone B and tryptone provides nitrogenous, carbonaceous compounds and other essential growth nutrients.