Cronobacter has one characteristic: relatively stable α-glucosidase activity.

This enzyme is not unique to Cronobacter, but the vast majority of Cronobacter strains exhibit α-glucosidase activity, making it an important biochemical identification indicator for this genus. If we add a substrate that can be specifically recognized by this enzyme into the culture medium, the target bacteria will “actively expose” themselves during growth.

This substrate is X-α-Glc.

Its full name is 5-bromo-4-chloro-3-indolyl α-D-glucopyranoside. One end of the molecule is an indole chromophore, and the other end is α-D-glucose, connected by an α-glycosidic bond.

When the α-glucosidase produced by Cronobacter encounters X-α-Glc, the enzyme precisely cleaves this glycosidic bond and releases an indole intermediate. The intermediate itself is colorless, but under aerobic conditions it rapidly oxidizes and dimerizes to form a water-insoluble blue-green precipitate.

The precipitate stays in place and does not diffuse. Where the colony is, the color is there.

After 18–24 hours of culture, Cronobacter forms blue-green colonies, while other bacteria do not show blue-green color, allowing preliminary identification directly by colony color.

This is the core logic of DFI agar. X-α-Glc is one of the core chromogenic substrates in the DFI chromogenic system.

Chinese name: 5-Bromo-4-chloro-3-indolyl α-D-glucopyranoside

English name: 5-Bromo-4-chloro-3-indolyl α-D-glucopyranoside

Abbreviation: X-α-Glc

CAS No.: 108789-36-2

Molecular Formula: C14H15BrClNO6

Molecular Weight: 408.63

Specification: 1 g / 5 g / 25 g (custom packaging supported)

Appearance: off-white crystalline powder

Catalog No.: G01010002

Color: blue-green

1. Cronobacter DFI Agar Detection

For rapid screening and identification of Cronobacter (formerly Enterobacter sakazakii) in infant formula, dairy products, and production environment samples.

Mainly used for:

• Cronobacter detection in infant formula

• Microbial monitoring of dairy products and production environment samples

• Formulation development of DFI agar chromogenic medium

• Routine screening by food safety testing institutions

2. Development of Rapid Microbial Identification Media

Used to develop selective chromogenic media, rapid identification media, and multi-target differential media by utilizing differences in α-glucosidase activity among microorganisms.

Mainly used for:

• Substrate screening for rapid identification media

• Combination design of multi-color chromogenic media

• Differential identification of target and non-target bacteria based on enzyme activity differences

3. Development of Chromogenic Media for Pathogens Such as Staphylococcus aureus

Used for the development of selective chromogenic media in clinical/food microbiological testing to achieve direct identification of target colonies.

Mainly used for:

• Development of chromogenic medium for Staphylococcus aureus

• Food microbiological testing

• Formulation optimization of selective chromogenic media

When a chromogenic substrate moves from laboratory formulation to industrial production, the conditions it needs to meet are far more complex than “being able to develop color.” GeneSeqTools Bioscience & Technology's X-α-Glc provides support for medium development and production in the following aspects:

✅ Mature application system, formulation development has a basis

X-α-Glc is a classic chromogenic substrate for Cronobacter selective media such as DFI agar, and has long-term application accumulation in international standard methods and commercial products. Researchers can directly refer to mature systems for formulation design and optimization, reducing the time cost of exploring from scratch.

✅ Precipitating signal, clear colony localization

The blue-green precipitate generated after hydrolysis is insoluble in water and will not diffuse in the medium. Colony boundaries are distinct, making it easy to count and pick single colonies for subsequent confirmation. Plates can be stored and reviewed for a short time, suitable for laboratory quality control and result traceability.

✅ Low background, weakly positive colonies are not easily missed

The substrate has high purity, and before hydrolysis there is no background color development in the medium system, resulting in low background interference. An obvious chromogenic signal is produced only when the target enzyme is present, helping improve the contrast between target colonies and background.

✅ Domestic supply, more controllable delivery time and cost

Compared with imported brands, GeneSeqTools Bioscience & Technology provides localized prices and shorter delivery times. Batch-to-batch stability has been verified by a quality control system, supporting stable supply from small-scale research batches to industrial scale.