Bacteriology
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CHROMOGENIC CULTURE MEDIA
WHAT IS CHROMOGENIC CULTURE MEDIA?
Chromogenic Agar Media are culture medium used to isolate, identify, and differentiate specific microorganism from a heterogeneous population. The medium contains chromogenic substrate which is utilized by the microorganism to give colored colonies that is specific for each microorganism. Depending on the color of the result, the presence or absence of target organism is determined and also accurately differentiated from others.
Principal:
Chromogenic media contains soluble colorless molecules called chromogens. Chromogens are composed of two parts: a substrate ( which is the target of a specific enzymatic activity of the microorganism) and a chromophore.
When the bond between the substrate and chromophore is split by a specific enzyme produced by the target microorganism, chromophore is released. In its unconjugated form, the chromophore shows distinctive colour. Due to reduced solubility, chromophore forms a precipitate that imparts unique color to the colony.
Advantages of Use of Chromogenic Agar Media:
- 1/ Less Labor intensive and more economic: Though people perceive chromogenic media as expensive alternative, use of a single chromogenic medium rather two-three selective ones, reduces the cost of sample processing. Chromogenic media may eliminate the need of subculture and further biochemical test for the identification of the isolates.
2/ Less time consuming: As chromogenic media eliminate various steps of sample processing (e.g. subculturing, biochemical testing) results are available within 24 hours as compared to 48 hours or more by conventional methods. Timely diagnosis not only ensures better outcome for the patients but also helps in prevention and spread of infections.
3/ Easy identification: On chromogenic agar medium, target colonies of specific microorganisms can be recognized by their colour at a glance. No specialized equipment needed.
Most of the commercially available chromogenic media utilize substrates like indoxyl and its halogenated derivatives, metal chelators like Esculin, 8‐Hydroxyquinoline, substrates for β‐glucosidase enzyme etc. Based on these a number of companies have formulated several variations depending on need and usage.
specimens: such as urine, faeces, blood, tissues, swabs taken from skin and wound infected sites can be directly cultured on to the chromogenic agar with results from 18 to 24 hour incubation.
CHROMagarListeria, L. monocytogenes colonies adopt a specific blue colour surrounded by a white opaque halo.
CHROMagar E.coli is a culture medium which directly marks E. coli colonies in blue colour.
CHROMagar MRSA easily detects MRSA including low level resistant strains as mallow colour colonies.
CHROMagar Staph aureus has unrivalled sensitivity and specificity for detecting S. aure…
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STORAGE:
On receipt, store plates in the dark at 2 to 8°C.
PRECAUTIONS:
For professional use only, Do not use plates if they show evidence of microbial contamination, discoloration, drying, cracking or other signs of deterioration.
APPLICATION:
- 1-Chromogenic agars in the direct isolation and identification of pathogens in clinical specimens
- 2-Chromogenic detection and screening for resistance and toxins in microorganisms
- 3-Chromagar candida for rapid screening of clinical specimen for candida albican
