Identification should be performed as rapidly as possible. Since the vast majority of urinary tract infections are caused by E. coli, a rapid test should be used to identify red colonies from MacConkey agar.
β-Glucuronidase test for rapid identification of E. coli1
1 KILIAN, M. & BÜLOW, P. Rapid diagnosis of Enterobacteriaceae. I. Detection of bacterial glycosidases. Acta pathologica et microbiologica scandinavica. Section B, 84: 245-251 (1976).
1. Prepare a dense milky suspension of the organism to be tested in a small tube containing 0.25 ml of saline. The suspension should be prepared from colonies growing on MacConkey agar.
2. Add one tablet of 4-nitrophenyl-β-D-glucopyranosiduronic acid (PGUA) for detection of β-glucuronidase activity. Place a stopper in the tube and agitate vigorously for a few seconds.
3. Incubate the tube at 35-37 °C for 4 hours.
4. The development of a yellow colour in the supernatant indicates a positive test for E. coli.