Chromogenic Media for Food and Water Tests
The principle of chromogenic media is that a chromogenic substrate is split by an enzyme that is characteristic of the target organism into a sugar component and a chromogen. In the presence of oxygen the chromogen forms a dimer that colors the broth or the typical colony. The chromogenic substrates used in Chromocult® media confer clearly distinguishable colors to different colony types, allowing clear differentiation and identification of the microorganisms.
Chromocult® Coliform Agar is a selective and differential chromogenic culture medium intended for use in microbiology laboratories that analyze food and water. Within 24 hours this medium enables the detection, differentiation and enumeration of Escherichia coli and coliforms from drinking water and processed food matrices. A careful selection of inhibitors used in the selective media ensures the growth and recovery of these microorganisms. Chromocult® Coliform Agar contains Tergitol® 7 as an inhibitor of gram-positive bacteria which has no negative effect on the growth of the targeted coliforms / E.coli. Chromocult® Coliform Agar is therefore the ideal medium for the detection of coliforms or E.coli in drinking water and processed foods.Chromocult® Coliform Agar Data Sheet
Chromocult® Coliform Agar ES is a selective medium for the simultaneous detection and colony count of total coliforms and E.coli in fresh foods as well as in waste water samples. The combination of carefully selected peptones and the buffering capacity of MOPS create ideal conditions for rapid growth of coliforms and support an optimal transformation of the chromogenic substrates. Bile salts and propionate largely inhibit growth of accompanying gram-positive and gram-negative flora. The simultaneous detection of total coliforms and E. coli is achieved by using the combination of two specific chromogenic substrates. For the perfect sample preparation, MilliporeSigma provides Sodium Chloride Peptone Broth (buffered) and the Peptone Water (buffered).
Chromogenic media for the detection of coliforms in the food and beverages industries.
ISO 9308 part 1 (2014) specifies a detection method for Escherichia coli and coliform bacteria in water with a low bacterial background flora (e.g. drinking water and disinfected pool water). The method is based on membrane filtration and use of a chromogenic coliform agar medium. The selective and differential properties of the chromogenic coliform agar (CCA) reduce testing time to 24 hours, from 48 hours with the previous Lactose TTC agar method. The chromogenic substrates Salmon-GAL and X-glucuronide enable easy differentiation and enumeration of Escherichia coli and coliform bacteria, as both use characteristic enzyme combinations to cleave these substrates and grow as distinct coloured colonies. Enumeration of Escherichia coli includes all ß-D-galactosidase and ß-D-glucuronidase positive colonies (oxidase positive), which appear as dark-blue to violet. Enumeration of total coliforms includes all dark-blue and oxidase negative colonies with pink to red color.
ISO 11133 (2014) specifies a method to test culture media used for membrane filtration. Following filtration of a defined inoculated liquid, the membrane filter is placed on the surface of the tested agar. The productivity of the agar-membrane filter set is calculated compared to a reference media. The process must be repeated after every change of the membrane filter batch and /or agar batch, considerably increasing the workflow and costs for the customer. We offer certified ReadyPlate™ 55 KIT CCA, which contains ready to use 55 mm media plates and EZ-Pak® Membrane Filters. ReadyPlate™ 55 KIT CCA is compliant to ISO 11133 (2014) and ISO 9308 part 1 (2014), thereby reducing customer quality control costs for membrane filter and agar batch testing. The scope of this comparison study was to evaluate the productivity performance of the chromogenic coliform agar-membrane filter sets, which are currently available on the market.Read the full study.