Detection of specific bacterial enzymes by high contrast metal chelate formation. Part II. Specific detection of Escherichia coli on multipoint-inoculated plates using 8-hydroxyquinoline-beta-D-glucuronide.

The use of 8-hydroxyquinoline-beta-D-glucuronide for the demonstration of beta-glucuronidase activity within the family Enterobacteriaceae has been investigated. The compound has been shown to be an effective substrate for the bacterial enzyme and the Michaelis constant for the association has been determined. A multipoint-inoculated method was employed to test 400 routine clinical isolates including those of urinary and faecal origin. When grown on an agar-based medium containing the substrate together with a ferric salt, glucuronidase-positive organisms were revealed by intense black pigmentation located only in the colony mass. The only organism yielding positive results by this method was Escherichia coli. The shigellae tested were negative by this procedure. Of the total biochemically profiled E. coli organisms 80% were specifically visualised by the method. This contrasts with 97% positively obtained by a fluorescence procedure involving use of 4-methylumbelliferone-beta-D-glucuronide but which also gives positive results with Shigella sonnei. A simple, cost-effective procedure involving use of both techniques for specific detection of E. coli is described.