Analysis of Black Fungal Biofilms Occurring at Domestic Water Taps (I): Compositional Analysis Using Tag-Encoded FLX Amplicon Pyrosequencing

Abstract

Mass growth of dark fungal biofilms on water taps and associated habitats was observed in various German drinking water distribution systems recently. Customers of affected drinking water systems are anxious about potential and unknown health risks. These environments are known to harbour a fungal flora also comprising a variety of fungal opportunists that are well known to cause superficial mycoses in humans (Exophiala equina, Exophiala lecanii-corni) but are not known to establish dark biofilms so far. To gain profound insight on composition of respective biofilms, a metagenomic approach using Tag-Encoded FLX Amplicon Pyrosequencing (TEFAP) of the ribosomal internal transcribed spacer 2 region in comparison with a classical cultivation approach using Sabouraud agar with chloramphenicol and erythritol-chloramphenicol-agar was performed. E. lecanii-corni was found to be the major component in 10 of 13 biofilms analysed independently of the method used. Alternaria sp., E. equina, Fusarium spp. and Ochroconis spp. were also relatively abundant. As expected, TEFAP usually revealed a higher diversity than the cultivation approaches. For example, opportunistic species like Candida albicans or Exophiala dermatitidis were detected in very low amounts. In conclusion, TEFAP turned out to be a promising and powerful tool for the semi-quantitative analysis of fungal biofilms. Referring to relevant literature, potential biological hazards caused by fungi of the dark biofilms can be regarded as low.

From Glacier to Sauna: RNA-Seq of the Human Pathogen Black Fungus Exophiala dermatitidis under Varying Temperature Conditions Exhibits Common and Novel Fungal Response

“…Examinations of bathwater and sludge in drainpipes that are warmed daily to over 42°C have identified several species of this medically important genus [20]. Recently, mass growth of dark fungal biofilms on water taps and associated habitats was observed in various German drinking water distribution systems [21,22]. Here, E .…”

Fungal Contaminants in Drinking Water Regulation? A Tale of Ecology, Exposure, Purification and Clinical Relevance

“…Thus, the presence of fungi in groundwater associated with degradation of plant debris is limited or reported less often. On the other hand, oligotrophic conditions support growth of melanised fungi, such as Aureobasidium melanogenum , high diversity of Exophiala species and Rhinocladiella similis (Table 1) [9,11,19,23,26,66,67]. These species were regularly reported from different European countries from both ground- and tap water, but were rarely reported in a relation to surface water, pointing toward groundwater as the main source of contamination of tap water with these opportunistic pathogenic fungi (Table 1) [19].…”

“…Fungal biofilms were fully formed within 48 h from the beginning of an experiment mimicking real conditions in tap systems [132]. The presence of fungi in in vivo biofilms from tap systems in private homes, hospitals or industrial network was confirmed for opportunistic and pathogenic species from the genera Aspergillus , Candida , Exophiala , Fusarium , Malassezia , Ochroconis , Penicillium , Phialophora , Phoma and Rhinocladiella [23,26,27,31,133,134]. Once established, biofilms are difficult to be fully removed from the pipe system, which on the long-term leads to altered taste and odour of water, production of allergenic or irritating compounds, and mycotoxins with an effect on human health (Figure 1) [2,21].…”

“…During the production of tap water, cleaning processes including techniques for removing large particles from raw water, and addition of chlorine contribute to a lower load of fungi. Yet, some species remain present in tap water, later establishing biofilms that persist in water distribution systems [22,23]. Reservoirs before elevation stations, positive pressures in building distribution designs, preventive maintenance, permanent running water in the system and adequate residual disinfectant are examples of how the distribution system should be operating [24,25].…”

“…Presence of fungi in biofilms and their interactions with other microorganisms remain poorly understood, even though in recent years the use of metagenomic approaches brought more detailed insight to this field [23,26,27]. Fungi growing in biofilms inside taps and in tap water affect the taste and odour, interfering with the chlorination process, due to the release of a large scale of products known as secondary metabolites.…”