Abstract
Currently there are no evidence-based ecological measures for prevention of overgrowth and subsequent infection by fungi in the oral cavity. The aim of this study was to increase our knowledge on fungal–bacterial ecological interactions. Salivary Candida abundance of 82 Dutch adults aged 58–80 years was established relative to the bacterial load by quantitative PCR analysis of the Internal Transcribed (ITS) region (Candida) and 16S rDNA gene (bacteria). The salivary microbiome was assessed using barcoded pyrosequencing of the bacterial hypervariable regions V5–V7 of 16S rDNA. Sequencing data was preprocessed by denoising and chimera removal, clustered in Operational Taxonomic Units (OTUs) and assigned to taxonomy. Both OTU-based (PCA, diversity statistics) and phylogeny-based analyses (UniFrac, PCoA) were performed. Saliva of Dutch older adults contained 0–4 × 108 CFU/mL Candida with a median Candida load of 0.06%. With increased Candida load the diversity of the salivary microbiome decreased significantly (p<0.001). Increase in the Candida load correlated positively with class Bacilli, and negatively with class Fusobacteria, Flavobacteria, and Bacteroidia. Microbiomes with high Candida load were less diverse and had a distinct microbial composition towards dominance by saccharolytic and acidogenic bacteria - streptococci. The control of the acidification of the oral environment may be a potential preventive measure for Candida outgrowth that should be evaluated in longitudinal clinical intervention trials.
Highlights
In the decades healthcare services are faced with an aging population
After random picking of the subset of 800 reads per sample, 300 Operational Taxonomic Units (OTUs) remained in the dataset with an average 43 (SD 13; min 11, max 73) OTUs per sample (Dataset S1)
The subsampled reads were classified into 12 phyla (Table S1), with Firmicutes dominating the dataset (57% of reads), followed by Actinobacteria (20%), Bacteroidetes (14%) and Proteobacteria (7%)
Summary
In the decades healthcare services are faced with an aging population. In the European Union the proportion of 65 year and older is predicted to reach 53% of the total population by the year 2025 [1]. An aging population forms a health risk group due to several factors. There are internal factors such as senescence of tissues (e.g., mucosal fragility) and senescence of functions (e.g., lowered immune response). There are extrinsic factors such as polypathologies (e.g., diabetes and malignancies), polymedications and malnutrition [2]. The internal and external factors, which contribute to changes during aging, may disturb the balance in the oral microbial ecosystem. A disturbance in the oral homeostasis between bacteria and fungi (e.g., Candida) may cause oral infectious disease
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