Chromogenic culture media are culture medium used to isolate, identify and differentiate specific microorganisms from a heterogeneous population. The medium utilizes synthetic chromogenic enzyme substrates to specifically target pathogenic species or groups of species based on their enzyme activity.
Most chromogenic media are therefore both selective and differential, accommodating the inhibition of non-target organisms such as using antibiotics or other inhibitors and enabling target pathogens to grow. As only target pathogens generate colonies of a particular color, this reduces the number of colonies that require investigation within a polymicrobial culture. The use of different chromophore and metabolite derivatives then makes it possible to detect diverse enzyme activities all in one assay.
The benefits of using chromogenic media include faster results, reliable visual detection and additional testing possible directly from the media. Compared with the use of conventional culture media, this often results in cost savings from reduced labor time and reduced use of reagents as fewer biochemical and/or serological confirmation tests are required.
This also contributes to quicker confirmation of pathogens and reduces the overall time required to issue a report. In some cases, discrimination of target pathogens from background flora due to the generation of a specific color makes pathogens less likely to be overlooked, thus improving rates of detection.
In summary, the benefits of this method include:
Because chromogenic media is considered an alternative method, it needs to be validated following IS0 16140-1&2 and by the customer following ISO1640-3.
As with other methods, chromogenic media will at times give false positives from organisms that are showing similar biochemical reactions. Since this is a manual-based method of reading, there is the potential of human error and you need to trace incidences manually as compared to automated systems.
The average time-to-result for chromogenic media is 48 hours. While this makes it faster than traditional methods, it is still slower than some other alternative methods like polymerase chain reaction (PCR) and immunology. Another drawback of this is that as incubate plates are still required in this approach, incubator space is still necessary, unlike the PCR or immunology methods.
The major food pathogens that can be screened using chromogenic media including salmonella, campylobacter, listeria, listeria monocytogenes and E. coli.
The exact methodology can vary according to the sample matrix and frequently involves pre-enrichment for 24 hours or more. This ensures that any pathogen contamination is allowed time to resuscitate and achieve sufficient numbers to ensure that organisms are transferred on to the chromogenic medium when a subsample is plated out. There are also media available for specific application areas such as bacillus cereus, vibrio parahaemolyticus and enterobacter sakazakii found in infant formulae, yeasts and molds.
The culture media solutions and detection kits for microbiology laboratories that DKSH offers our customers include products from Biokar Diagnostics, Thermo Fisher Scientific and BioMérieux. Reach out to us to find out more on how these solutions can help elevate your business to the next level.
Julien Pastor is the new Director, Business Development, Food & Beverage, Business Unit Technology. Julien brings with him 14 years of relevant working experience across industries such as Food & Beverage, Veterinary, Pharma and Biotechnology. Julien ran his own consulting business with focus on food & pharma lab solutions creating digital content on YouTube and LinkedIn for global clients. Before that he held different regional positions at Becton Dickinson, Qiagen and BioMerieux and was the Chief Commercial Officer for Argolight.