TABLE 1.

Comparison of sample collection dates, DNA extraction kits, library preparation and high-throughput sequencing methodologies for the PPG and PG analyzed in this study.

Group	Pre-pandemic (PPG)	Pandemic (PG)
Year	2016	2020
Sample collection dates
DNA extraction kit	QIAamp DNA Stool Mini Kit (QIAGEN®) and Quick-DNA Soil (Zymo Research®)*	QIAamp-PowerFecal DNA-Kit (QIAGEN®)
Target region	16S gene hypervariable region V3-V4	16S gene hypervariable region V3-V4
Primers	Bakt_341F/Bakt_805R	Bakt_337F/Bakt_805R
Library preparation methodology	Herculase II Fusion DNA Polymerase Nextera XT Index Kit V2 (Illumina® 16S Metagenomic Sequencing Library Preparation Part # 15044223 Rev. B)	Herculase II Fusion DNA Polymerase Nextera XT Index Kit V2 (Illumina® 16S Metagenomic Sequencing Library Preparation Part # 15044223 Rev. B)
NGS chemistry (paired-end approach)	Illumina® MiSeq v3 (2 × 300)	Illumina® MiSeq v3 (2 × 300)
Sequences per sample (mean ± SD)	111620.15 ± 9328.76	82752.34 ± 7925.77

*All 23 stool samples were subjected to DNA extraction by both methods.

SD, standard deviation.