Stool collection and DNA extraction
STERILE, LYSIS
The participants collected a fecal sample (50–60 g) 3 ± 7 days [mean ± standard deviation] prior to the positron emission tomography/computed tomography (PET/CT). They transported the fecal sample in plastic sterile containers inside a portable cooler until arrival at the research centre. Fecal samples were stored at −80 °C until the extraction of deoxyribonucleic acid (DNA). A QIAamp DNA Stool Mini Kit (QIAGEN, Barcelona, Spain) was utilized to extract DNA following the manufacturer’s instructions, and samples were incubated at 95 ºC to ensure lysis of both Gram-positive and Gram-negative bacteria. The quantification of DNA was performed using a NanoDrop ND1000 spectrophotometer (Thermo Fisher Scientific, DE, USA). We measured absorbance spectrophotometrically at A260/280 nm and A260/230 nm ratios for determining DNA purity. The A260/280 ratio is used to determine protein contamination [