Pathogenic yeast strains prefer city air

The air in Hong Kong contains pathogenic strains of Candida yeast, the presence of which was not detected in air samples from the seaside, reports the journal Environmental Science & Technology Letters.

A trip to the seaside offers not only a relaxing change of scenery and a chance to reset your mind, but also the opportunity to breathe cleaner air than that of the big city. Doctors have traditionally recommended seaside trips for the treatment of illnesses (thalassotherapy). And almost a decade ago, wealthy Chinese suffering from smog began purchasing clean air from ocean-bound New Zealand in handy pressurized bottles capable of holding 180 breaths.

New research provides another reason to visit the coast. It was conducted by an international team including scientists from The Hong Kong Polytechnic University, Nanjing University, and East China Normal University (China), Imperial College London (UK), and Freie Universitat Berlin (Germany). Hong Kong's urban air has been found to contain pathogenic strains of the yeast Candida, which were not found in air samples from coastal areas. It's possible that infections from this fungus could be airborne.

Candida yeasts are a group of common microorganisms that live harmlessly on human skin and in the lining of internal organs. However, under certain conditions, they can overgrow and cause conditions such as vaginal yeast infections or oral thrush. These infections are known to spread through direct contact or bodily fluids. However, previous studies have shown the presence of Candida DNA in the air, suggesting that these yeasts are capable of airborne transmission.

So the researchers searched for viable infectious strains of Candida in air samples from urban and coastal areas. Samples were collected in Hong Kong and a nearby, less populated town overlooking the South China Sea, once a month throughout the year.

Three Candida species classified by the World Health Organization as fungal pathogens were detected in 12 air samples from urban areas: C. albicans, C. parapsilosis, and C. tropicalis. However, samples collected from coastal areas did not contain detectable levels of Candida. This difference between locations suggested that the airborne yeasts could originate, for example, from municipal wastewater treatment plants.

Several air samples from urban areas contained pathogenic Candida species that are resistant to commonly used antifungal drugs. Scientists suggest that overuse of antifungal drugs, pollutants such as heavy metals, or increased air temperature may contribute to this resistance. Finally, the genetic makeup of one of the airborne Candida strains was closely related to samples previously collected from people infected with Candida, suggesting that these airborne strains may be infectious.

According to the authors, their work challenges the long-standing assumption that Candida is transmitted primarily through direct contact, presenting this yeast as a novel airborne pathogen. However, further research is needed to investigate the origins of urban Candida and understand precisely how infectious it can be when airborne.

Paweł Wernicki (PAP)

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