The oral microbiota is closely associated with systemic health, but few studies have investigated the oral microbiota in patients with obstructive sleep apnea (OSA). This study aimed to identify the variation of oral microbiota among patients withsevere OSA, and the change of oral microbiota after treatment withcontinuous positive airway pressure (CPAP). Participants were enrolled in the studyfrom November 2020 to August 2021. Sleep parameters using full nocturnal polysomnography (PSG) were collected on healthy controls, patients withsevere OSA, and patients withsevere OSA after CPAP treatment for 3months. Oral samples were also collected by rubbing disposable medical sterile swabs on the buccal mucosa. Routine blood tests and biochemical indicators were measuredusing the fully automated biochemical analyzer. Oral microbial composition of oral samples were determinedusing whole-genome metagenomic analysis in all participants. Correlations were analyzedbetween the oral microbiota and blood lipids. Study enrollment included 14 participants, 7 healthy controls and 7 patients with severe OSA.At the species level, the relative abundances of Prevotella, Alloprevotella, Bacteroides, Veillonella_tobetsuensis, Candidatussaccharimonas, and Leptotrichia in the groups withsevere OSA were significantly lower than those in the healthy controls (P both < 0.05). The abundances of Capnocytophaga, Veillonella, Bacillus_anthracis, Eikenella, and Kingella were significantly higher whereas the abundances of Gordonia and Streptococcus were significantly lower in the group withsevere OSA compared to the severe OSA-CPAP group (P < 0.05 for both). According to the Kyoto Encyclopedia of Genes and Genomes (KEGG), 4 pathways changed in the group withsevere OSA compared with healthy controls (P both < 0.05). Pathways related to Novobiocin biosynthesis, 2-Oxocarboxylic acid metabolism, and Histidine metabolism were enriched in thepatients with severe OSA. Nine pathways showed significant differences with regard to the relative abundances of phenylalanine metabolism; alanine, aspartate, and glutamate metabolism; one carbon pool by folate; monobactam biosynthesis; 2-oxocarboxylic acid metabolism; arginine biosynthesis and vitamin B6 metabolism; novobiocin biosynthesis; and arginine and proline metabolism, which were significantly higher in the group withsevere OSA compared to the severe OSA-CPAP group (P both < 0.05). The Spearman correlation analysis between blood lipid parameters and oral microbiota components showed that negative correlations were observed between total cholesterol and Streptomyces (r = - 0.893, P = 0.007), and high-density lipoprotein cholesterol (HDL-C) and Gordonia (r = - 0.821, P = 0.023); positive correlations were observed between HDL-C and Candidatus saccharimonas (r = 0.929, P = 0.003), and low-density lipoprotein cholesterol (LDL-C) and Capnocytophaga (r = 0.893, P = 0.007). There was an apparent discrepancy of the oral microbiota and metabolic pathways between the group withsevere OSA and controls, and CPAP significantly changed oral microbial abundance and metabolic pathways in patients with severe OSA. Correlation analysis showed that these oral bacteria were strongly correlated with the blood lipids level.
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