DISCUSSION
STERILE, CAVITY, DRUG EFFECT
The core findings of our study are that airway microbiota of healthy volunteers show resilience and abilities for recovery from azithromycin perturbation. There is a depletion of family In our study, we found that exposure to azithromycin resulted in decreases in the detection rate and relative abundance of different genera belonging to In contrast, the relative abundance of taxa belonging to PMWe performed network analysis to support the above-mentioned assumption. The functional stability of microbial communities depends on the complicated microbe-microbe interactions (Our study has following limitations. First, we use induced sputum to investigate the variation in airway microbiota after antibiotic intervention. The induced sputum is a variable mixture that may contain materials from human airways and oral cavities. We asked the subjects to fast for 4 to 6 h and clean their oral cavity. To determine the contribution of each source, oral washes were also performed by having the subjects gargle with 10 mL sterile 0.9% saline for 60 s immediately before sputum induction. We found that the bacterial DNA load in oral wash samples is significantly lower than sputum samples (Fig. S11). Although the oral wash samples are commonly used in oral cavity microbiota studies, the bacterial load being lower in the oral wash may be the result of sample dilution. The oral cavity microbiota has higher species richness and a significantly different microbial community composition compared to sputum microbiota. Compared to the sputum microbiota, the oral cavity microbiota has a different change pattern and recovers earlier after antibiotic exposure (Fig. S12 to S16). However, for successful 16S rRNA gene library preparation, we increased the volume of oral wash samples up to 3 mL for DNA extraction. This is not consistent with the volume of the induced sputum (750 μL), which may decrease the comparability of the sequencing data.Second, the human airway microbiome may be influenced by numerous factors. For example, there was a lack of some data on diet and its possible effects on the airway or oral microbiota. To avoid deviations as much as possible, we strictly executed a randomized, double-blind, placebo-controlled pattern across the entire study and experimentation process. The stability in airway microbiota of the placebo group subjects gave us evidence to believe our conclusions drawn from the azithromycin group. Third, we did not explore the relationship between the antibiotic resistance and airway microbiota. It is important to figure what or how the streptococci resist the drug effect and how they lose it following re-establishment of the microbial structure, but the study design of this paper could not answer that. In a future study, we will focus on this important question. At last, we followed up with the volunteers for only 60 days; the longer-term effects after azithromycin administration demand more attention in future.