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Debaryomyces hansenii and Anti-Candida Activity
Debaryomyces hansenii is the most common yeast species found in cheese, and is able to produce killer toxins that have displayed activity against human pathogenic fungi Candida species in the lab. Several studies have reported D. hansenii in the human gastrointestinal (GI) tract. In order to characterize killer toxin, D. hansenii was grown under toxin-producing conditions and secreted proteins were concentrated, purified, and tested for activity. The molecular mass of the purified killer toxin was estimated to be 11.10 kDa sharing a sequence homology with a thioredoxin protein. All Candida albicans and C. tropicalis strains tested were sensitive with purified D. hansenii killer toxin. Purified D. hansenii killer toxin displayed higher activity at the acidic pH (4.5 and below) and lower temperatures (20 and 25 C), while the killer activity duration was for only a short time (3 hours) when purified killer toxin was incubated at 37 C. The presence of sodium chloride (NaCl) enhanced killer activity. The fungal community in the GI tract was then characterized and evaluated for the influence of D. hansenii present naturally in cheese on gut Candida populations. Six human subjects consumed 50 g of cheese containing D. hansenii daily for five days in a pilot study. Fungi were identified using MiSeq sequencing of ITS gene tags. The fungal abundance in the six subjects during the baseline period was dominated by phylum Ascomycota (99.26%). At the family level, Debaryomycetaceae contributed nearly a quarter of detected taxa, (24.16%) followed by Nectriaceae at 22.15% and Saccharomycetaceae at 17.51%. Saccharomyces (17.23%) was the predominant genus present. Other genera detected were Fusarium (16.07%), Debaryomyces (15.12%), Candida (9.01%), Dekkera (6.84%), Gibberela (6.08%), Dendryphiella (5.87%), Acremonium (5.6%), and Penicillium (1.02%). Candida abundance decreased with the consumption of cheese containing D. hansenii as compared to baseline but no statistically significant difference was observed. Furthermore, a negative correlation between the Candida and Debaryomyces abundance. However, the strength of the correlation was weak (R=0.39). The significance of this result shown that the possibility that D. hansenii may influence gut Candida populations and thus could be a feasible Candidate to combat C. albicans overgrowth and virulency.
Banjara, Nabaraj, "Debaryomyces hansenii and Anti-Candida Activity" (2017). ETD collection for University of Nebraska - Lincoln. AAI10684419.