  Indoor microbial diversity and composition are suggested to affect the
prevalence and severity of asthma. In this study, we collected floor dust and
environmental characteristics from 21 classrooms, and health data related to
asthma symptoms from 309 students, in junior high schools in Johor Bahru,
Malaysia. Bacterial and fungal composition was characterized by sequencing 16s
rRNA gene and internal transcribed spacer (ITS) region, and the absolute
microbial concentration was quantified by qPCR. In total, 326 bacterial and 255
fungal genera were characterized. Five bacterial (Sphingobium, Rhodomicrobium,
Shimwellia, Solirubrobacter, Pleurocapsa) and two fungal (Torulaspora and
Leptosphaeriaceae) taxa were protective for asthma severity. Two bacterial
taxa, Izhakiella and Robinsoniella, were positively associated with asthma
severity. Several protective bacterial taxa including Rhodomicrobium,
Shimwellia and Sphingobium has been reported as protective microbes in previous
studies, whereas other taxa were first time reported. Environmental
characteristics, such as age of building, size of textile curtain per room
volume, occurrence of cockroaches, concentration of house dust mite allergens
transferred from homes by the occupants, were involved in shaping the overall
microbial community but not asthma-associated taxa; whereas visible dampness
and mold, which did not change the overall microbial community for floor dust,
decreased the concentration of protective bacteria Rhodomicrobium
(\b{eta}=-2.86, p=0.021) of asthma, indicating complex interactions between
microbes, environmental characteristics and asthma symptoms. Overall, this is
the first indoor microbiome study to characterize the asthma-associated
microbes and their environmental determinant in tropical area, promoting the
understanding of microbial exposure and respiratory health in this region.
