HiCrome Candida Differential Agar: Introduction, Principle, Test Requirement, Procedure, Result-Interpretation, and Keynotes

Introduction

HiCrome™ Candida Differential Agar is a specialized chromogenic medium used in clinical microbiology for the rapid isolation and presumptive identification of Candida species. The medium is designed to differentiate between major Candida species—Candida albicans, Candida tropicalis, Candida krusei (Pichia kudriavzevii), and Candida glabrata—based on colony color and morphology within 48 hours. It is especially useful in laboratories with limited resources, as it can replace more time-consuming conventional tests like the germ tube test and sugar fermentation. 

Principle

Enzymatic Activity: The agar contains chromogenic substrates that react with specific enzymes produced by different Candida species. For instance, Candida albicans produces N-acetyl-galactosaminidase, which reacts with the chromogens to produce a distinct color. Selectivity: It includes Chloramphenicol, which inhibits the growth of most accompanying bacterial flora. Nutritional Support: Peptone and yeast extract provide essential nitrogenous and carbonaceous compounds for yeast growth. 

Test Requirements

• Medium (HiCrome™ Candida Differential Agar)
• Equipment: Sterile Petri plates, incubator (30-35°C), and standard inoculating tools.
• Specimens: Clinical samples such as skin scrapings, urine, high vaginal swabs, blood cultures, pure isolate

Procedure

1. Preparation: Suspend approximately 42.72 grams of the medium in 1000 ml of distilled water. Heat to boiling to dissolve completely. Do not autoclave.
2. Inoculation: Aseptically streak or surface-spread the clinical specimen onto the prepared agar plates.
3. Incubation: Incubate the plates aerobically at 30-35°C for 40 to 48 hours. 

Result Interpretation

Presumptive identification is based on the final color and morphology of the colonies: 

Candida Species	Colony Appearance
Candida albicans	Light green, smooth colonies
Candida tropicalis	Blue to metallic blue, raised colonies
Candida krusei	Purple, fuzzy, dry/flat colonies
Candida glabrata	Cream to white, smooth, glistening colonies
Candida parapsilosis	Cream to pale pink, glistening colonies

Keynotes

• Presumptive Identification: Colors provide a presumptive diagnosis; definitive identification for some species may require supplementary biochemical tests.
• Storage: Store the dehydrated powder between 15-25°C and prepared plates at 2-8°C away from light.
• Limitations: Variations in color intensity can occur depending on the specific enzyme activity of the isolate. Other filamentous fungi may also produce color on this medium. 

Further Readings

1. https://www.himedialabs.com/in/m1297a-hicrome-candida-differential-agar.html
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC11357716
3. https://www.ijcmr.com/uploads/7/7/4/6/77464738/evaluation_of_hicrome_candida_differential_agar_for_species_identification_of_candida_isolates_from_various_clinical_samples.pdf
4. https://www.nepjol.info/index.php/JCMSN/article/view/29896/24168
5. https://www.airchecklab.com/services/microbial-id
6. https://www.researchgate.net/figure/Photograph-of-Candida-species-as-seen-on-HiCrome-agar-a-Cream-coloured-glistening_fig5_341180383
7. https://www.scribd.com/document/888476576/Hi-Chrome-Agar-Technical-Sheet
8. https://journals.lww.com/ijpm/fulltext/2010/53010/hichrom_candida_agar_for_identification_of_candida.20.aspx
9. https://utoronto.scholaris.ca/server/api/core/bitstreams/98849705-b5f8-429c-99ec-a8f969930773/content