Human microbiota drives indoor air microbes
Résumé
Which element is shared the most by humans? It is neither food nor water, it is air. This enforced sharing, a potential vector of many diseases, has increased exponentially in recent years because of changes to our lifestyle. To date, the microbial content of air in enclosed spaces has been little described. Environmental data resulting from an investigation of sources and pathogens are extremely rare, despite their health implications. Our study addressed these issues. In this context, the aim of this study was to characterize the bacterial diversity of indoor air, and in particular to highlight ‘core species’, opportunistic pathogens and origin of indoor bacteria found in three different enclosed spaces with three levels of occupancy (low: office, high: museum and average: hospital). A sampling device that could be connected to existing ventilation system of the building was developed. The measurements of indoor bioaerosols were performed during four-weeks sampling periods in 2010. The three buildings, Lagny hospital, office in Champs-sur-Marne and Louvre Museum are located in Paris or Paris suburbs, France. We used high-throughput sequencing of the bacterial 16S rRNA gene in order to describe airborne bacterial communities of these three indoor environments. Our findings provided an overall description of bacterial diversity in these indoor environments. The results of sequencing of the data collected on three enclosed spaces revealed a common microflora (more than 60% of all sequences).This work will enable a clearer understanding of the dominant groups of bacteria encountered in enclosed spaces: Actinobacteria, Proteobacteria, Firmicutes and Bacteroidetes. Thus, some evidence enabled a connection between ‘core species’ and the human microenvironment (20% of phylotypes and 12% of sequences of human origin). Global PCA analysis showed that the indoor environment might mostly be influenced by nasal and skin microbial diversity. Among the ‘core species’ found during this study, a large number (72% of all pathogen-related sequences were concentrated in ‘core species’) of genera and species are known to be responsible for opportunistic or nosocomial diseases, or include human commensal bacteria such as Mycobacterium sp., Acinetobacter baumanii, Aerococcus viridians, Thermoactinomyces vulgaris or Clostridium perfringens. In conclusion, indoor air is much stables that outdoor air. This stability over time and within different buildings can be explained by the human origin of most of the indoor air microbe whatever the ventilation system used. Thus, indoor air can be considered as a part of the human microbiota and as the way to exchange fecal, skin, nasal etcetera and pathogen microbes. Today, at least 50% of the world population is urban and spend more 90% of their time in a tiny bubble of indoor air. This fact relatively new for human being must take in account at the sanitary level as example through pathogen emergence or bioterrorism.