Cortisol Promotes Surface Translocation of Porphyromonas gingivalis

The oral microbiome is associated with HPA axis response to a psychosocial stressor

Intense psychosocial stress during early life has a detrimental effect on health-disease balance in later life. Simultaneously, despite its sensitivity to stress, the developing microbiome contributes to long-term health. Following stress exposure, HPA-axis activation regulates the "fight or flight" response with the release of glucose and cortisol. Here, we investigated the interaction between the oral microbiome and the stress response. We used a cohort of 115 adults, mean age 24, who either experienced institutionalisation and adoption (n = 40) or were non-adopted controls (n = 75). Glucose and cortisol measurements were taken from participants following an extended socially evaluated cold pressor test (seCPT) at multiple time points. The cohort´s oral microbiome was profiled via 16S-V4 sequencing on microbial DNA from saliva and buccal samples. Using mixed-effect linear regressions, we identified 12 genera that exhibited an interaction with host's cortisol-glucose response to stress, strongly influencing intensity and clearance of cortisol and glucose following stress exposure. Particularly, the identified taxa influenced the glucose and cortisol release profiles and kinetics following seCPT exposure. In conclusion, our study provided evidence for the oral microbiome modifying the effect of stress on the HPA-axis and human metabolism, as shown in glucose-cortisol time series data.

An outer membrane vesicle specific lipoprotein promotes Porphyromonas gingivalis aggregation on red blood cells

Porphyromonas gingivalis uses a variety of mechanisms to actively interact with and promote the hydrolysis of red blood cells (RBCs) to obtain iron in the form of heme. In this study, we investigated the function of lipoprotein PG1881 which was previously shown to be up-regulated during subsurface growth and selectively enriched on outer membrane vesicles (OMVs). Our results show that wildtype strain W83 formed large aggregates encompassing RBCs whereas the PG1881 deletion mutant remained predominately as individual cells. Using a PG1881 antibody, immunofluorescence revealed that the wildtype strain's aggregation to RBCs involves an extracellular matrix enriched with PG1881. Our findings discover that RBCs elicit cell aggregation and matrix formation by P. gingivalis and that this process is promoted by an OMV-specific lipoprotein. We propose this strategy is advantageous for nutrient acquisition as well as dissemination from the oral cavity and survival of this periodontal pathogen.

Evaluation of hydrocortisone as a strain-dependent growth-regulator of Porphyromonasgingivalis

OBJECTIVE

Porphyromonas gingivalis is an oral key pathogen and known to be very diverse in geno- and phenotypes. It is a fastidious bacterium with low O₂-tolerance and 3-7 days of incubation are necessary. With growing interest in the field of microbial endocrinology we explored the potential growth-stimulating effect of hydrocortisone (HC, synonym cortisol) on P. gingivalis cultures.

MATERIAL AND METHODS

Six different P. gingivalis strains were pre-incubated in supplemented Brain-Heart-Infusion broth under appropriate conditions for 24 h, diluted and transferred into microplates. A newly developed and semi-automated spectrophotometric measurement in triplicate, applying a SpectraMax i3x microplate reader at an optical density of 600 nm, was conducted to test growth differences between test group (exposed to a supplement of either 1.25, 2.5, 5, 10, or 20 μg/ml of hydrocortisone) and control group over 48 h of anaerobic incubation (O₂ ≤ 1%). Furthermore, strains were also incubated on HC-supplemented blood agar to test for a possible growth-stimulating effect on solid media.

RESULTS

HC significantly stimulated the lag-phase growth of four out of six P. gingivalis strains. Our data suggest a concentration-dependent growth stimulatory effect of HC between 2.5 and 5 μg/ml, while below 1.25 μg/ml and above 10 μg/ml HC either did not stimulate or inhibited growth.

CONCLUSIONS

HC could reduce the incubation time when isolating P. gingivalis from clinical samples and could boost low biomass cultivations especially during their lag-phase. The growth-modulating effect might be via modulation of virulence factors/quorum sensing gene expression or by reactive oxygen species(ROS)-capturing during early stages of bacterial growth. Further experiments are necessary to explain the mechanism behind our observations.