Table 1.

In vitro and in vivo studies focusing on the effect of psychological stress on the oral microbiome.

Experiment	Results	Reference
In vitro
Samples of dental plaque treated with cortisol and performed metatranscriptomic analysis	Cortisol directly induced shifts in the gene expression profiles of the oral microbiome that reproduce results found in the expression profiles of periodontal disease and its progression. Members of the phylum Fusobacteria (class Fusobacteria and order Fusobacteriales) showed significantly increased activity (increased the number of transcripts significantly) after the addition of cortisol.	[55]
Volatile sulfur-producing oral bacteria treated with mucin and cortisol	Mucin increased the viability of F. nucleatum. Cortisol did not affect S. moorei and F. nucleatum.	[56]
Volatile sulfur-producing oral bacteria treated with adrenaline, noradrenaline, and cortisol	Adrenaline, noradrenaline, and cortisol significantly reduced F. nucleatum growth after 12 h and 24 while reduced Porphyromonas endodontalis growth after 24 h. Prevotella intermedia and Porphyromonas gingivalis showed no effects on bacterial growth.	[57]
43 microorganisms of subgingival microbial complexes treated with noradrenaline and adrenaline	Noradrenaline treatment showed positive growth in Actinomyces naeslundii, Actinomyces gerenscseriae, Eikenella corrodens, and Campylobacter gracilis. Noradrenaline treatment inhibited P. gingivalis and B. forsythus. Responses to adrenaline tended to mirror the responses seen with noradrenaline.	[58]
Noradrenaline treated with P. gingivalis	Dose-dependent inhibition of P.gingivalis by noradrenaline was seen at 24 h and 36 h of treatment.	[59]
In vivo
Fecal glucocorticoid metabolites, a measure of hypothalamic–pituitary–adrenal axis correlated with the oral microbiome in wild red squirrel using 16 S rRNA gene sequencing	Alpha diversity of the oral microbiome was lower in individuals with elevated fecal glucocorticoid metabolites. Relative abundance of oral Pasteurellaceae increased with increasing fecal glucocorticoid metabolites.	[60]
Evaluation of oral microbiome in chronic restraint stress using rat	Alpha diversity of the oral microbiome was significantly reduced in the stress group. Facklamia was increased while Corynebacterium was decreased in the stress group.	[61]