Rapid Identification of Enterococci with a New Fluorogenic-Chromogenic Assay

Enterococci are used as indicators of faecal contamination of water and food and are commonly detected using kanamycin-aesculin-azide media. Aesculin can be enzymatically hydrolysed at the β-glucose linkage to yield two products: aesculetin and glucose. Aesculetin produces a brown-black coloured compound with ferric ions. Enterococci give a positive reaction with this test but some other microorganisms can also give positve results and can be mis-identified as enterococci thus making confirmation important. A simple filter paper strip test has been developed to detect pyroglutamyl aminopeptidase and β-D-glucosidase using fluorogenic L-pyrroglutamic acid 7-amido-4-methyl-coumarin and chromogenic 5-bromo-4-chloro-3-indolyl-β-D- glucopyranoside. In contrast to the commonly used PYR test, the newly developed method needs no additional reagents. The method was found to be very successful for the rapid and specific identification of enterococci in water samples.