Dishwashers--a man-made ecological niche accommodating human opportunistic fungal pathogens

Habitats in human households may accommodate microorganisms outside the common spectrum of ubiquitous saprobes. Enrichment of fungi that may require specific environmental conditions was observed in dishwashers, 189 of which were sampled in private homes of 101 towns or communities. One-hundred-two were sampled from various localities in Slovenia; 42 from other European countries; 13 and 3 from North and South America, respectively; 5 from Israel; 10 from South Africa; 7 from Far East Asia; and 7 from Australia. Isolation was performed on samples incubated at 37°C. Species belonging to genera Aspergillus, Candida, Magnusiomyces, Fusarium, Penicillium and Rhodotorula were found occasionally, while the black yeasts Exophiala dermatitidis and Exophiala phaeomuriformis (Chaetothyriales) were persistently and most frequently isolated. Sixty-two percent of the dishwashers were positive for fungi, and 56% of these accommodated Exophiala. Both Exophiala species are known to be able to cause systemic disease in humans and frequently colonize the lungs of patients with cystic fibrosis. We conclude that high temperature, high moisture and alkaline pH values typically occurring in dishwashers can provide an alternative habitat for species also known to be pathogenic to humans.