Abstract: 9223 A. Introduction

Enzyme substrate tests use hydrolyzable chromogenic and fluorogenic substrates to simultaneously detect enzymes produced by total coliforms and Escherichia coli. In this method, total coliform bacteria produce the enzyme β-d-galactosidase, which cleaves the chromogenic substrate in the medium to release chromogen. Most E. coli strains produce the enzyme β-glucuronidase, which cleaves a fluorogenic substrate in the medium to release fluorogen. The release of chromogen indicates that coliform bacteria are present, and the release of fluorogen indicates that E. coli are present.

Multiple-tube, multiwell, or presence-absence (single 100-mL sample) formats are available for use with these enzyme substrate tests.