Known chromogenic enzyme substrates such as X-Gal (B-7150) and Magenta-beta-D-Gal (B-7200) form bacteria colonies with colors ranging from blue to red on solid (agar) media. This limitation of the available colors may impede the simultaneous detection of multiple enzymes on one agar plate. Therefore, we developed new substrate colors: Jalapeño green-Gal, Bronze-Gal, Crimson-Gal, and Espresso-Gal. These substrates rapidly develop colored colonies of beta-galactosidase positive bacteria E. coli and coliforms.
Detection of E. coli using the novel beta-galactosidase substrate Espresso-Gal (E-3650). Nutrient agar plates were inoculated with a mixed cell suspension of beta-galactosidase positive E.coli and beta-galactosidase negative Salmonella enteritidis. Spread-plate method using 0.5 mM Espresso-Gal.Incubation: 24 hrs at 37°C.
Find more application examples of our new colors in the "New Colors for Microbiologists" handout.
Info: Chromogenic Substrates in Microbiology
Specific enzymes produced by the target micro-organism cleave a chromogenic substrate, liberating the chromophor, which highlights the micro-organism by coloration of the grown colony.
The principle of bacteria detection using their specific enzyme activity. Beta-Galactosidase positive Escherichia coli and X-Gal as one example: 1. Uptake of the substrate X-Gal by E. coli cells. 2. Enzymatic cleavage of the substrate. 3. Formation of a blue-turquoise chromophore due to the dimerization and oxidation of the enzyme product 5-bromo-4-chloro-3-hydroxyindole.
As a result, in the presence of X-Gal colonies of E. coli will appear in dark blue on agar plates.
The new colors for beta-Galactosidase detection handout (1 MB PDF)
Our four new substrates generate colors that are clearly different from conventional substrates and can be combined with conventional substrates on solid culture media to detect multiple enzyme activities simultaniously.
For an overview of conventional chromogenic substrates and target enzymes please see our
Table of Substrates for Bacteria Assays
Download: Application Note
Cultural Response Tests using Chromogenic and Fluorogenic Substrates