DNA extraction
Total DNA was isolated from 1 µL of purified control bacterial strains using a TIANamp bacteria DNA kit (TIANGEN Biotech, Beijing, China) following the manufacturer’s instructions. Plasma was obtained by centrifuging the blood sample at 1,600 × g for 20 min. Plasma DNA extraction was isolated from 2 mL plasma using a magnetic serum/plasma DNA kit (TIANGEN Biotech, Beijing, China) and the Auto-Pure20B nucleic acid purification system (Hangzhou Allsheng Instruments, Zhejiang, China). DNA was eluted in 50 μL of elution buffer, and stored at -80oC until use.