Changes in salivary microbiota increase volatile sulfur compounds production in healthy male subjects with academic-related chronic stress

Objective
To investigate the associations among salivary bacteria, oral emanations of volatile sulfur compounds, and academic-related chronic stress in healthy male subjects.
Materials and methods
Seventy-eight healthy male undergraduate dental students were classified as stressed or not by evaluation of burnout, a syndrome attributed to academic-related chronic stress. This evaluation was carried out using the Maslach Burnout Inventory—Student Survey questionnaire. Oral emanations of hydrogen sulfide, methyl mercaptan, and dimethyl sulfide were measured using an Oral Chroma™ portable gas chromatograph. The amounts in saliva of total bacteria and seven bacteria associated with halitosis were quantified by qPCR. The in vitro production of H2S by S. moorei and/or F. nucleatum was also measured with the Oral Chroma™ instrument.
Results
The stressed students group showed increased oral emanations of hydrogen sulfide and dimethyl sulfide, together with higher salivary Solobacterium moorei levels (p < 0.05, Mann Whitney test). There were moderate positive correlations between the following pairs of variables: Fusobacterium nucleatum and S. moorei; F. nucleatum and hydrogen sulfide; Tannerella forsythia and F. nucleatum; T. forsythia and S. moorei. These correlations only occurred for the stressed group (p < 0.05, Spearman correlation). The in vitro experiment demonstrated that S. moorei increased H2S production by F. nucleatum (p < 0.05, ANOVA and Tukey’s test).
Conclusion
The increased amount of S. moorei in saliva, and its coexistence with F. nucleatum and T. forsythia, seemed to be responsible for increased oral hydrogen sulfide in the healthy male stressed subjects.

研究目标：以健康男性为研究对象，探讨唾液菌群、口腔挥发性硫化物释放量与学业相关性慢性应激三者之间的关联。

材料与方法：招募78名健康男性口腔医学专业本科学生，以职业倦怠（burnout，一种由学业相关性慢性应激引发的综合征）作为评估指标，将受试者分为应激组与非应激组。评估采用马斯拉奇职业倦怠量表-学生版（Maslach Burnout Inventory—Student Survey）问卷进行。采用Oral Chroma™便携式气相色谱仪检测受试者口腔释放的硫化氢、甲硫醇及二甲基硫含量。通过实时荧光定量PCR（quantitative PCR, qPCR）定量检测唾液中总细菌及7种与口臭相关的细菌载量。同时采用Oral Chroma™仪器检测摩尔氏嗜糖杆菌（Solobacterium moorei, S. moorei）和/或核梭杆菌（Fusobacterium nucleatum, F. nucleatum）的体外硫化氢生成量。

结果：应激组学生的口腔硫化氢、二甲基硫释放量显著升高，唾液中摩尔氏嗜糖杆菌载量亦显著升高（曼-惠特尼U检验，p < 0.05）。变量间存在中等程度正相关的组合包括：核梭杆菌与S. moorei、核梭杆菌与硫化氢、福赛斯坦纳菌（Tannerella forsythia, T. forsythia）与核梭杆菌、福赛斯坦纳菌与S. moorei；且上述相关性仅在应激组中存在（斯皮尔曼相关性分析，p < 0.05）。体外实验结果显示，S. moorei可增强F. nucleatum的硫化氢生成能力（方差分析+图基多重比较检验，p < 0.05）。

结论：健康男性应激受试者唾液中S. moorei载量升高，且其与F. nucleatum和T. forsythia共存，可能是导致口腔硫化氢水平升高的原因。