The Relation between Oral <em>Candida</em> Load and Bacterial Microbiome Profiles in Dutch Older Adults

<div><p>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 <em>Candida</em> 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 (<em>Candida</em>) 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 <em>Candida</em> with a median <em>Candida</em> load of 0.06%. With increased <em>Candida</em> load the diversity of the salivary microbiome decreased significantly (<em>p</em><0.001). Increase in the <em>Candida</em> load correlated positively with class Bacilli, and negatively with class Fusobacteria, Flavobacteria, and Bacteroidia. Microbiomes with high <em>Candida</em> 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 <em>Candida</em> outgrowth that should be evaluated in longitudinal clinical intervention trials.</p>