The aim of this chapter is to provide an insight into use of enzyme substrates, and to help microbiologists to make informed choices, whether they intend to design, make media according to the formulae in this book, or purchase these types of media.

The use of chromogenic and fluorogenic substrates has increased dramatically in the 20 years since the Association of Official Analytical Chemists (AOAC) approved the use of lauryl tryptose broth with 4-methylumbelliferyl-β-D-glucuronide for presumptive identification of Escherichia coli in foods (Moberg et al., 1988). There have been many good reviews on the use of chromogenic and fluorogenic substrates in culture media over the years (Manafi et al., 1991; Dealler, 1993; Manafi, 1996, 2000, 2003; Perry and Freydiere, 2007). These reviews have concentrated on the breadth of application of the technology. This chapter focuses on the depth in an attempt to build upon the work of these other reviews.