Hidden things lurking in sink drains can be dangerous, even deadly: ScienceAlert

Sink drains and plumbing fixtures are generally unpleasant places, at least from a human perspective.

However, if you are a fungus, you may feel differently. In fact, one of the reasons why we are often put off by sinks – along with dirty mushrooms and other sink accessories – it’s precisely because they’re such great habitats for nasty germs.

In a new study by researchers from the University of Reading and the UK’s Center for Ecology and Hydrology, scientists dove deep into this murky ecosystem, examining more than 250 “toilet sink fungal communities” on a university campus.

Led by University of Reading bioinformatician Sun Gweon, the research team collected samples from toilet sink drains and P-traps in 20 buildings on the university’s main campus.

The researchers used sterile cotton swabs to sample drains and P-syphons, recording details about the qualities of each sink, including its location, purpose, bathroom gender label, and whether the water flowing into the drain was hot or cold. Extracting DNA from the samples, they used polymerase chain reaction (PCR) amplification and bioinformatics to help identify the microbial inhabitants of the sinks.

The results showed moldy jungles with a variety of fungi, like small rainforests in the sewers.

It might seem obvious that damp places like these would do it support the life of microbes, but the mere presence of fungi is not the main conclusion. These fungal communities are diverse, the researchers report, but also remarkably similar to one another.

The sinks contained 375 genera of fungi – the taxonomic rank above species – from a range of classes, orders and families. The study found fungi representing seven different phyla, a taxonomic rank below kingdom.

Despite the high biodiversity in each sink, all fungal communities showed surprisingly similar taxonomic profiles, the researchers reportmeaning the mushroom list and ratio doesn’t vary much from sink to sink or even building to building.

The researchers note that they’re not sure what’s driving this similarity, but keep in mind that similarity in sink fungi from different latrines and buildings may reflect “similar use” by people in the community.

All of these sinks are used primarily for hand washing, with many of those using the facilities coming from the wider university population and any of them could be exposed to the germs when using the sinks.

“We spend 90 percent of our time indoors, so we are exposed to fungi in our homes and workplaces,” Gueon says.

“For most people this is not a problem, but for those who are immunocompromised, some types of fungus can cause serious infections.”

The study suggests that sink drains and P-traps aren’t just nice places for microbes to live, but can serve as reservoirs for some molds, yeasts and other fungi, potentially harboring and aiding the spread of species that can make people sick .

“It is not a big surprise to find fungi in warm, moist environments. But sinks and P-sinks have so far been overlooked as potential reservoirs of these microorganisms,” Gweon says.

“This could be a really important finding for those trying to help immunocompromised people avoid infections from some of the opportunistic pathogens that may be lurking in sinks, such as fusarium.”

Sink drains and pipes offer a unique habitat for fungi in the built environment, Gweon and his colleagues Notedue to constant moisture, temporary temperature changes, high pH from detergents and potential build-up of organic matter.

However, the sponges in the sinks should also be tough. They face blasts of hot water, for example, plus fluctuating levels of acidity and food availability. Some fungi may use the detergents in the soap as a carbon-rich food source, the researchers suggest.

The most abundant and ubiquitous genus found in the new study was Exophialathe researchers report, “black yeast,” which includes both terrestrial and aquatic species.

“Exophiala species can be considered opportunistic pathogens causing skin and surface infections,” they write. They may not pose a high risk overall, but “fatal systemic infections have been documented.”

The study was published in Environmental DNA.