HiCrome™ UTI HiVeg™ Agar

Principle And Interpretation

Urinary tract infections are bacterial infections affecting parts of urinary tract. The common symptoms of urinary tract infection are urgency and frequency of micturition, with associated discomfort or pain. The common condition is cystitis, due to infection of the bladder with a uropathogenic bacterium, which most frequently is Escherichia coli, but sometimes Staphylococcus saprophyticus or especially in hospital-acquired infections, Klebsiella species, Proteus mirabilis, other coliforms, Pseudomonas aeruginosa or Enterococcus faecalis (1). HiCrome® UTI Agar is formulated on basis of work carried out by Pezzlo (2) Wilkie et al (3), Friedman et al (4), Murray et al (5), Soriano and Ponte (6) and Merlino et al (7). HiCrome® UTI HiVeg® Agar is same as HiCrome® UTI Agar except that the animal based peptones are completely replaced with vegetable peptones to avoid the BSE/TSE risks associated with animal peptones. These media are recommended for the detection of urinary tract pathogens where HiCrome® UTI Agar has broader application as a general nutrient agar for isolation 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. The chromogenic substrates are specifically cleaved by enzymes produced by Enterococcus species, E.coli and coliforms. Presence of amino acids like phenylalanine and tryptophan from peptones helps for detection of tryptophan deaminase activity, indicating the presence of Proteus species, Morganella species and Providencia species.

One of the chromogenic substrate is cleaved by β-glucosidase possessed by Enterococci resulting in formation of blue colonies. E.coli produce pink colonies due to the enzyme β-D-galactosidase that cleaves the other chromogenic substrate. Further confirmation of E.coli can be done by performing the indole test. Coliforms produce purple coloured colonies due to cleavage of both the chromogenic substrate. Colonies of Proteus, Morganella and Providencia species appear brown because of tryptophan deaminase activity. Peptone special provides nitrogenous, carbonaceous compounds, long chain amino acids, vitamins and other essential growth nutrients. This medium can be made selective by supplementation with antibiotics for detecting microorganisms associated with hospital borne infections.