The Candida genus includes numerous yeasts that humans can use biotechnologically. For example, Candida famata belongs to the group of those fungi that, in addition to causing dangerous infections, can also be used to produce useful products such as riboflavin (vitamin B). Normally, however, it is a commensal, a companion of humans and other living organisms that lives relatively frugally on byproducts and waste products of metabolism.
What is Candida famata?
The genus Candida belongs to the true yeasts of the class Saccharomycetes and is classified as a tubular fungus. However, it does not form fruiting bodies, but exists as an asexual division form that changes to a sexual growth form (teleomorph) only under certain environmental conditions. For a long time, C. famata was considered to be an anamorph (asexual form) of a yeast called Debaryomyces hansenii, and the two varieties C. famata var flareri and C. famata var famata were distinguished. However, these could be genetically assigned to separate species, so that C. famata var flareri can now be assigned to the yeast Debaryomyces subglobosus as Candida flareri. Because of this separation, it is necessary to verify that all previous research statements regarding C. famata were really made for this species and not for its sister species. The species is highly salt tolerant and grows in media up to 2.5 M NaCl. In addition, it has the ability to produce riboflavin in the presence of iron deficiency (flavinogenic yeast).
Occurrence, distribution, and characteristics
C. famata is common in the environment and is most easily extracted from processed foods, especially cheese and other dairy products. It is also encountered in clinical contexts, where it is found primarily skin-associated. The yeast forms white to cream-colored round colonies with a smooth surface on agar. The cells are ovoid in shape (2.0-3.5 x 3.5-5.0 µM) and do not form pseudohyphae. Instead, they reproduce via budding or blastoconidia. It is capable of metabolizing glucose, galactose, maltose, sucrose, trehalose, D-xylose, melezitose, glycerol, raffinose, cellobiose, L-arabinose, and sugar alcohols, among others. Negative assimilation tests are available for potassium nitrate and inositol. Thus, infection in the classical sense does not occur when infection with C. famata occurs. Rather, in most cases the yeast grows completely inconspicuously on the skin of healthy people. Only a weakening of the immune system can result in dangerous multiplication, which can then spread to the blood and other organs of the affected person.
Significance and function
The fact that C. famata produces increased amounts of riboflavin when iron is deficient can be explained by a survival advantage. Presumably, the yeast uses this substance as an electron donor for iron reduction or directly as a cofactor for extracellular and intracellular enzymes. The osmotolerance/halophily of this species can also be exploited by culturing under high salt conditions. This allows competitive microorganisms that can only tolerate lower salt levels to be displaced. In this way, a quasi-sterile culture management can be established. Since sterile technology is a major cost factor for biotechnological processes, this significantly increases efficiency when using C. famata. It is obvious to use this yeast for riboflavin production, which has been further optimized by genetic engineering (especially overexpression of enzymes involved in riboflavin production). Other potential applications are in the synthesis of flavin mononucleotide (FMN) and flavin dinucleotide (FAD).
Diseases and disorders
Infections with C. famata usually follow the pattern of classical candidiasis, that is, skin and mucous membranes (e.g., in the mouth/digestive tract or intimate area) are most commonly colonized. Mild forms of only superficial candidiasis are often observed as a result of changes in the skin or intestinal flora, e.g. after antibiotic treatments. Hygienic deficiencies or misuse of skin-irritating cosmetics can also promote this form of infection. Furthermore, pregnancies or hormonal contraceptives can have an influence specifically on the vaginal environment and reduce its acidity, resulting in less protection against the growth of yeasts.Due to the fact that it is a facultative pathogen, a severe previous weakening of the immune system due to other diseases such as HIV, diabetes, cancer, sepsis or immunosuppressive treatment with e.g. cytostatics or cortisone must be assumed in the case of very severe infections. C. famata can also invade the bloodstream and from there attack other organ systems up to the central nervous system. Other infections described included catheter-transmitted systemic candidiasis, peritonitis, mediastinitis, and acute zonal occult [[retinopathy]s. Diagnosis is usually made microscopically from a smear or culture of blood, urine, or cerebrospinal fluid. It has proven problematic in this regard that the usual morphologic/phenotypic identification of cultures obtained from infectious material sometimes leads to misidentification. In this case, C. famata was often identified, although the pathogen at hand was a different Candida species. Due to the different susceptibility to antimycotics, suboptimal treatment approaches result here. Different therapies are used depending on the site of infection: Disinfecting ointments and sprays as well as mycostatic silver preparations can be used on the skin surface. In addition, yeasts can be treated like any other fungal infection with antimycotics. Locally, azoles such as clotrimazole or isoconazole are mainly used for this purpose, while ketoconazole, fluconazole or nystatin, for example, are used for systemic therapy. Particularly severe cases of organic infections can be treated with infusions of 5-fluorocytosine or amphotericin B. Prevention of C. famata infection is analogous to all other candidiases: in immunosuppressed patients, antifungal agents can be used prophylactically. In the intimate area, improvements in the microenvironment may be achieved by wearing moisture-wicking underwear-this also applies to infants with a tendency to diaper candidiasis.
