Saliva samples were stored at -80C. Then, DNA extraction was performed using the ZymoBIOMICS DNA extraction kit (Zymo Research, 2023) following the manufacturer's instructions. The extracted DNA from each sample was quantified using the DeNovix DS-11FX microvolume spectrophotometer. Samples were selected based on their concentration (> 2 ng/l) and their OD260/280 ratio (range between 1.8-2.0). The samples were sequenced at NovoGene using the Amplicon Metagenomics service (WOBI). For the amplification of the V3-V4 region of the 16S gene, primers 341F: CCTAYGGGRBGCASCAG and 806R: GGACTACNNGGGTATCTAAT were used. Sequencing was done using the Illumina NovaSeq platform (150 paired end reads).