design: DNA was extracted from swab samples using the Qiagen DNeasy Blood and Tissue kit. DNA was amplified using primers 341F (5-CCTACGGGNGGCWGCAG-3) and 805R (5-GACTACHVGGGTATCTAATCC-3), targeting the V3-V4 regions of the bacterial 16S rRNA gene. Amplicon libraries were sequenced on an Illumina MiSeq 2000 (Illumina, San Diego, CA, USA) using a 2 x 300 bp kit.