Candida Krusei

Candida Krusei is a fungal pathogen for those patients suffering with hematologic malignancies. From the family of Saccharomycotina, Candida krusei is a type of yeast which takes part in the process of the production of chocolate. This yeast has resistance towards fluconazole which is a genuine antifungal medication. It has been studied that it mostly occurs in those who had been exposed to fluconazole. Studies show that mortality in case of fungemia caused by Candida krusei is much more than those caused by the common fungi, Candida albicans.

 

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A study in 1991 aimed to detect whether there existed a relation between the introduction of fluconazole in patients with bone marrow transplantation and increase in the infection caused by C. krusei. A retrospective study was conducted based on the medical records, mycological records and autopsy reports in patients with bone marrow transplantation (total 296 cases) in the time period of 1989-1990. It was seen that although fluconazole successfully controlled C. albicans as well as C. tropicalis, it resulted in increase of the C. krusei flora.

This study revealed that although fluconazole is a well-known drug in treating Candida pathogens, when introduced in patients with bone marrow transplants was observed to enhance the growth of Candida Krusei. Hence, fluconazole is not the ideal medication for treating this type Candida species.

 

Electron microscopy of Candida Krusei
Electron microscopy of Candida Krusei
 

How is Candida Krusei Related with Chocolates?

How can a fungal yeast have any connection with the most delicious thing in this world can be a question in several minds! While producing chocolate, one of the indigenous and pre-requisite steps is to ferment the cacao beans. This fermentation process is required in order to take care of the excessive bitter taste and in order to disintegrate them. This fermentation occurs due to Candida krusei and also Geotrichum. In general, both these species exist both on the seeds as well as on the seed pods of cacao plant; however, in today’s modern art of manufacturing, particular methods are applied. Individual strains are utilized by different chocolate manufacturing companies which are selected on the basis of their flavor. The selection of the strain depends on the aroma that it will add to the finished chocolate. The yeast reproduces rapidly. The renewed multiplication occurs every few hours and within a short period of time, the yeast multiplies themselves into many so as to produce specific cells in smaller regions. This results in enzymes which help in the disintegration of the pulp on the exterior of the beans. This phenomenon produces acetic acid, which kills the cacao embryo resting inside the seed. The bitterness of the cacao beans immediately vanishes replacing it with the intense chocolate essence which the world adores!

 

Observations on Candida Krusei

  • Candida krusei is a MDR fungal pathogen and studies show that infections are eminent in those patients’ taking amphotericin B.
  • Response rate of this infection was better in case of those receiving amphotericin B of about ≥ 1mg/kg of the body mass each day than the ones with lower dosage.
  • Although it has an intrinsic resistance to fluconazole, Candida krusei is susceptible to voriconazole.

Candida krusei can be cured using voriconazole, caspofungin and amphotericin B.

 

In 1997 a study found that a triazole named as ‘voriconazole’ was successful in blocking sterol biosynthesis in two pathogenic strains of Candida, namely Candida albicans and Candida krusei. This observed the subinhibitory concentration of the drugs, fluconazole and voriconazole on the sterol biosynthesis process of both the strains of Candida. It resulted in the fact that although the albicans strain was susceptible to fluconazole the difference in sterol compositions, in case of susceptible and resistant strain, fluconazole was not significant. While in case or voriconazole, it was pretty evident and significantly less in both albicans and krusei.

This study shows clear evidence that indeed voriconazole is a better choice for the treatment of Candida albicans as well as krusei strain of Candida. It also shows that if a patient is affected with both the fungi’s, it can be successfully dealt with by using voriconazole which was not possible earlier.

 

Requirements for Candida Krusei

Candida krusei multiplies at a temperature around 43-45 degree Celsius. Candida krusei is somewhat different from the other species belonging to the same genus. Majority of the Candida species require biotin and other vitamins which help them grow and multiply, however, C. krusei grows in a vitamin starved environment. The other Candida species form convex colonies but Candida krusei develops on Sabouraud’s dextrose agar. It forms extensive colonies which has whitish-yellow media with roughness. This species when looked under the microscope appears like long grain rice. Therefore, the grain like appearance along with its matte surface helps in the easy identification of this species. When Candida krusei develops in culture medium constituting lactose, a large number of complex metabolites results with several fatty acids. When cultured in a medium of saliva including glucose, several short length carboxylic acids develop. It constitutes of propionate, succinate, formate, acetate, lactate and so on.

 

References:

Candida krusei, a Multidrug-Resistant Opportunistic Fungal – Journal of Clinical Microbiology – 2008 – By M. A. Pfaller, D. J. Diekema and D. L. Gibbs
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2238087/
 
Candida krusei: biology and epidemiology – Journal of Medical Microbiology – 1994 – By Yuthika H. Samaranayake and Lakshman P. Samaranayake
http://jmm.microbiologyresearch.org/content/journal/jmm/10.1099/00222615-41-5-295?crawler=true&mimetype=application/pdf
 
Candida krusei infection – New England Journal of Medicine – 1991 – By Wingard JR, Merz WG, Rinaldi MG
http://www.nejm.org/doi/pdf/10.1056/NEJM199110313251803
 
Biosynthesis in Candida albicans and Candida krusei – Antimicrobial Agents and Chemotherapy Journal – 1997 – By Sanati H, Belanger P,  Fratti R and Ghannoum M.
http://aac.asm.org/content/41/11/2492.short
 
Handbook of Proteolytic Enzymes – Volume 1 – Book by Alan J. Barrett, ‎J. Fred Woessner, ‎Neil D. Rawlings – 2012
 

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