Educational facilities serve as community hubs and consequently hotspots for exposure to pathogenic microorganisms.Therefore,it is of critical importance to understand processes shaping the indoor microbiomes in educational facilities to protect public health by reducing potential exposure risks of students and the broader community.In this study,the indoor surface bacterial microbiomes were characterized in two multifunctional university buildings with contrasting levels of human occupancy,of which one was recently constructed with minimal human occupancy while the other had been in full operation for six years.Higher levels of human occupancy in the older building were shown to result in greater microbial abundance in the indoor environment and greater proportion of the indoor surface bacterial microbiomes contributed from human-associated microbiota,particularly the skin microbiota.It was further revealed that human-associated microbiota had greater influence on the indoor surface bacterial microbiomes in areas of high occupancy than areas of low occupancy.Consistent with minimal impact from human occupancy in a new construction,the indoor microbiomes in the new building exhibited significantly lower influence from human-associated microbiota than in the older building,with microbial taxa originating from soil and plants representing the dominant constituents of the indoor surface bacterial microbiomes.In contrast,microbial taxa in the older building with extensive human occupancy were represented by constituents of the human microbiota,likely from occupants.These findings provide insights into processes shaping the indoor microbiomes which will aid the development of effective strategies to control microbial exposure risks of occupants in educational facilities.