Members of the Oral Microbiota Are Associated with IL-8 Release by Gingival Epithelial Cells in Healthy Individuals

Abstract

The triggers for the onset of oral diseases are still poorly understood. The aim of this study was to characterize the oral bacterial community in healthy humans and its association with nutrition, oral hygiene habits, and the release of the inflammatory marker IL-8 from gingival epithelial cells (GECs) with and without stimulation by bacterial endotoxins to identify possible indicator operational taxonomic units (OTUs) associated with inflammatory marker status. GECs from 21 healthy participants (13 females, 8 males) were incubated with or without addition of bacterial lipopolysaccharides (LPSs), and the oral microbiota was profiled using 16S rRNA gene-targeted sequencing. The basal IL-8 release after 6 h was between 9.9 and 98.2 pg/ml, and bacterial communities were characteristic for healthy oral microbiota. The composition of the oral microbiota was associated with basal IL-8 levels, the intake of meat, tea, white wine, sweets and the use of chewing gum, as well as flossing habits, allergies, gender and body mass index. Additionally, eight OTUs were associated with high basal levels of IL-8 and GEC response to LPS, with high basal levels of IL-8, and 1 with low basal levels of IL8. The identification of indicator bacteria in healthy subjects with high levels of IL-8 release is of importance as they may be promising early warning indicators for the possible onset of oral diseases.

Keywords: IL-8; healthy humans; inflammation; nutrition; oral microbiota.

FIGURE 1

Basal release of IL-8 by GECs after 6 h incubation (range: 9.9–98.2 pg/ml, mean: 42,4 pg/ml) depicted as a (A) scatter plot of residuals of all participants (n = 21). The solid line represents the mean value, the medium dashed line the specification level of mean ± 1 SD, the short dashed line the specification level of mean ± 2 SD. (B) QQ-Plots for low IL-8 group (n = 12) and high IL-8 group (n = 9).

FIGURE 2

Abundant bacterial taxa from gum brushes. (A) phylum-, (B) family-, and (C) genus-level taxon profiles are shown. Abundant taxa, defined as having a mean relative abundance of >1%, are shown.

FIGURE 3

Redundancy analysis of oral microbiota at OTU level. Parameters significant at OTU level in the perMANOVA analysis were plotted and are represented by arrows. The direction of the arrows shows the association between variables, in this case with meat and IL-8.

FIGURE 4

Dominant indicator OTUs are presented for pgLPS response with their relative abundance (as percent) for each sample. Each OTU is annotated with the closest reference sequence and the sequence similarity with the reference species. The indicator OTUs are grouped according to the condition for which they are an indicator for each combination. Each column of the heatmap represents a single sample.