Correlations between Microbial Diversity Indices and Quantities of Opportunistic Pathogen-related Taxa in Indoor Air

Indoor microbial exposure has been associated with occupant health; however, the interplay between community diversity and genus-level opportunistic pathogen-related indicators remains unclear. This study aimed to examine how microbial alpha diversity was associated with genus-level opportunistic pathogen-related indicators in indoor environments. Airborne bacterial and 18S-based eukaryotic communities from indoor and outdoor sites were characterized using 16S and 18S rRNA amplicon sequencing. Associations between four alpha-diversity indices and opportunistic pathogen-related estimated absolute abundance and relative abundance (RA) were evaluated using correlation and mixed-effects models, with supplementary segmented and compositionality-aware analyses. Significant differences were observed between indoor and outdoor opportunistic pathogen-related community structures. Diversity-related patterns differed between bacterial and fungal communities. In the main analyses, richness-related diversity metrics were positively associated with opportunistic pathogen-related estimated absolute abundance in both bacterial and fungal communities. However, these associations were not retained after adjustment for qPCR-based total microbial abundance, indicating that they were largely explained by variation in qPCR-based total microbial abundance rather than by alpha diversity itself. Relative-abundance-based patterns differed between bacterial and fungal communities and should be interpreted cautiously. These findings indicate that alpha-diversity metrics alone do not independently explain opportunistic pathogen-related estimated absolute abundance in indoor air and should instead be interpreted together with qPCR-based total microbial abundance.