DNA extraction and sequencing
DNA from saliva samples has been extracted using the ZymoBIOMICS™ DNA Mini Kit (Zymo Research, Irvine, California, United States) according to the manufacturer’s instructions. Elution was performed in 60 mL of RNAse-free water and resulting DNA was stored at −20°C prior to preparation for sequencing. All samples were subsequently normalized to a standard concentration of 1 ng/mL and a volume of 15 mL (for a total of 15 ng of DNA) prior to Illumina 16S sequencing (V3-V4) at KI SciLife Laboratory on MiSeq. The 16S rRNA analysis was performed using the nf-core/ ampliseq analysis pipeline (