Given that they occupy every other niche on earth, including deep sea vents, salt flats and the interior of human bodies, it should come as no surprise that bacteria are also found in human houses. Once inside, they can cause problems; airborne bacteria can be easily move between people and spread their corresponding diseases. Nowadays, with the proliferation of aircon units and indoor fans there are more ways than ever for airborne bacteria to be lifted up and spread around an indoor area.
A recent paper in PLOS ONE looks at how bacteria enter these indoor environments. There are various different routes they could potentially take: they could breeze in through open windows and doors, be actively carried on human skin or clothes, or be introduced through breathing, sneezing, or coughing in an enclosed space. The researchers chose a university classroom as their enclosed space, and performed quantitative analysis of the indoor bacteria, including those found on the floor, suspended in the air, and found in the aircon and ventilation units. These were then compared to phylogenetic libraries of bacteria found in the human skin microbiome, outdoor aerial bacteria, and indoor floor dust to see where the indoor bacteria were coming from.
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