Abstract
We investigated the diversity and distribution of fungi in nine different sites inside 30 residential dishwashers. In total, 503 fungal strains were isolated, which belong to 10 genera and 84 species. Irrespective of the sampled site, 83% of the dishwashers were positive for fungi. The most frequent opportunistic pathogenic species were Exophiala dermatitidis, Candida parapsilosis sensu stricto, Exophiala phaeomuriformis, Fusarium dimerum, and the Saprochaete/Magnusiomyces clade. The black yeast E. dermatitidis was detected in 47% of the dishwashers, primarily at the dishwasher rubber seals, at up to 106 CFU/cm2; the other fungi detected were in the range of 102 to 105 CFU/cm2. The other most heavily contaminated dishwasher sites were side nozzles, doors and drains. Only F. dimerum was isolated from washed dishes, while dishwasher waste water contained E. dermatitidis, Exophiala oligosperma and Sarocladium killiense. Plumbing systems supplying water to household appliances represent the most probable route for contamination of dishwashers, as the fungi that represented the core dishwasher mycobiota were also detected in the tap water. Hot aerosols from dishwashers contained the human opportunistic yeast C. parapsilosis, Rhodotorula mucilaginosa and E. dermatitidis (as well as common air-borne genera such as Aspergillus, Penicillium, Trichoderma and Cladosporium). Comparison of fungal contamination of kitchens without and with dishwashers revealed that virtually all were contaminated with fungi. In both cases, the most contaminated sites were the kitchen drain and the dish drying rack. The most important difference was higher prevalence of black yeasts (E. dermatitidis in particular) in kitchens with dishwashers. In kitchens without dishwashers, C. parapsilosis strongly prevailed with negligible occurrence of E. dermatitidis. F. dimerum was isolated only from kitchens with dishwashers, while Saprochaete/Magnusiomyces isolates were only found within dishwashers. We conclude that dishwashers represent a reservoir of enriched opportunistic pathogenic species that can spread from the dishwasher into the indoor biome.
Highlights
Over the last two decades, the incidence of fungal infections of humans has increased at an alarming rate, which already today presents a major challenge to health care systems
E. dermatitidis was isolated in only 2% of samples (1/44), while 10% were positive for other Exophiala species, including Exophiala alcalophila (1/44) and Exophiala lecanii-corni (3/44)
R. mucilaginosa and Cystobasidium slooffiae together were isolated from 2% (1/44) and 6% (3/44) of the water samples, Pseudozyma crassa and the F. dimerum species complex (FDSC) were both found in 5% (2/44) and 7% (3/44), respectively, of the samples, whereas other fungal species were isolated only sporadically
Summary
Over the last two decades, the incidence of fungal infections of humans has increased at an alarming rate, which already today presents a major challenge to health care systems. This correlates with the increased average age, the large number of people with treatable chronic diseases, the growing population of immunocompromised individuals, and the practices of intensive chemotherapy and use of immunosuppressive drugs [1,2,3]. As people spend more than 80% of their time indoors on average [5], many studies have examined the relationships between housing conditions and air-borne fungi, and how these relate to respiratory symptoms, such as asthma and fungal-related allergies [6,7,8,9]. The few studies on the distribution of fungi in residential kitchens have focussed on contamination with outdoor air-borne fungi [16,17,18], and on contamination of bathrooms and kitchen sinks by fungal biofilms in plumbing systems [13,14,15,19]
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