The data of 24 consecutive patients who underwent curative resection for rectal cancer with ileostomy by a laparoscopic approach at Juntendo University Hospital between November 2016 and June 2018 were reviewed in this retrospective study. The inclusion criteria were stage Ⅰ–Ⅳ cancer, lateral pelvic lymph node dissection, and previous treatment with neoadjuvant pelvic chemoradiotherapy and chemotherapy. Patients who underwent emergency surgery, those with synchronous cancers, and those who underwent abdominoperineal resection were excluded from the current study.
Most of the total and tumor-specific mesorectal excisions were performed by the same team of staff colorectal surgeons. By using ileum of 30-40cm from ileum end, Ileostomy were made on lower right abdominal wall. ileostomy stool samples were collected on postoperative day 7. Rectal anastomoses were performed using the double stapling technique in patients undergoing LAR. Reconstruction comprised hand-sewn coloanal anastomosis in patients undergoing ISR. In all patients, cancer staging was based on the eighth edition of the TNM classification of malignant tumors. The indications for loop ileostomy were the following: anastomosis < 5 cm from the anal verge, obstruction, neoadjuvant therapy, intraoperative technical issues, and severe diabetes mellitus. Preoperative neoadjuvant chemotherapy (such as FOLFOX or CapeOX) or chemoradiotherapy (such as S-1 with 45-Gy radiation) were administered in patients with cStage Ⅱ–Ⅲ rectal cancer according to the TNM classification.
No chemical preparations such as those including kanamycin and metronidazole were administered preoperatively.8,9 All patients were intravenously administered 3 g/day cefmetazole, a cephamycin antibiotic. The use of probiotics, such as Miya-BM containing Clostridium butyricum M588, was based on the surgeon’s discretion.
AL was defined by the following clinical criteria: pelvic abscess, fecal discharge from the wound and drain, septicemia, and peritonitis, with or without radiologically confirmed leakage.10 Grading of AL was performed as described by Rahbari et al. 11 Surgical site infections were defined using the U.S. Centers for Disease Control definitions.12 Postoperative ileus was defined as the inability to tolerate food in the presence of abdominal distension, absence of bowel sounds, and the need to delay enteral feeding.13 Grading was based on the Clavien–Dindo classification.14 High output was defined as an ostomy output ≥1500 mL, as described in previous studies.15,16
DNA extraction from stool samples and 16S rRNA sequencing
The ileal stool from the stoma pouch were suspended in 900 µL buffer containing 4M guanidium thiocyanate, 100 mM Tris-HCl (pH 9.0), and 40 mM ethylenediaminetetraacetic acid (pH 8.0) and centrifuged at 20800 g for 5 min. The supernatants were discarded, and 600 μl TE buffer (10 mmoL/L Tris-HCl pH 8.0, 1 mmoL/L ethylenediaminetetraacetic acid pH 8.0) was used to wash the pellets twice. Next, glass beads (diameter, 0.15–0.21 mm) were added, and the samples were homogenized at 7000 rpm for 20 s using a MagNA Lyser instrument (Roche, Penzberg, Germany). Next, 2 µL lysozyme (10 mg/mL; Wako, Osaka, Japan) was added, the samples were incubated for 1 h at 37℃. Next, 100 µL of 10% sodium dodecyl sulfate (Kanto Kagaku Tokyo, Japan) and 600 µL of the phenol/chloroform/isoamyl alcohol solution (Nippon Gene, Tokyo, Japan) were added, and the samples were processed at 7000 rpm for 20 s in the MagNA Lyser. Next, the samples were centrifuged at 20 800 g for 5 min, and 600 µl of the supernatants were transferred to 1.5-mL tubes, followed by the addition of 600 µL isopropanol and 60 µL of 3M sodium acetate (Nippon Gene). The samples were centrifuged at 20800 g for 5 min, and the supernatants were removed by decanting. The DNA pellets were washed with 70% ethanol, dried with a centrifugal evaporator (Eyela, Tokyo, Japan), and dissolved by incubating in 200 µL TE buffer and 2 µL RNase (1 mg/mL; Nippon Gene) for 1 h. The purity of the samples were determined with the High PCR template preparation kit (Roche, Basel, Switzerland). The DNA concentrations were quantified using the QuantiFluor One dsDNA system (Promega, Wisconsin, USA).
The variable V3–4 regions of the 16S rRNA gene were amplified by polymerase chain reaction using 341F (50-AATGATACGGCGACCACCGAGATCTACAC(adaptor sequence) + barcode (eight bases)+ACACTCTTTCCCTACACGACGCTCTTCCGATCT (sequence primer) + CCTACGGGNGGCWGCAG-30) and 805R primers (50-CAAGCAGAAGACGGCATACGAGAT(adaptor sequence)+ barcode (eightbases) + GTGACTGGAGTTCAGACGTGTGCTCTTCCGATCT (sequenceprimer) + GACTACHVGGGTATCTAATCC-30)and the Takara Ex Taq® Hot Start Version kit (Takara, Otsu, Japan). The amplicons generated from the samples were purified using SPRIselect (Beckman Coulter, Pennsylvania, USA). The DNA concentrations of purified amplicons were quantified using the QuantiFluor One dsDNA system, and equal DNA amounts were pooled.
The pooled samples were sequenced using Miseq Reagent kit V3 (600-cycle; Illumina, San Diego, CA, USA) on the Miseq system according to the manufacturer’s instructions. Sequence data were analyzed using the Quantitative Insights into Microbial Ecology (QIIME) pipeline (version1.9.1).
Determination of α-diversity and β-diversity
The number of observed species and Chao1 and Shannon phylogenetic diversity indices were calculated using the R package “phyloseq” and statistically analyzed using Wilcoxon’s test. β- diversity was estimated using the UniFrac metric to calculate the distances between the samples and visualized by principal coordinate analysis. The graphs were generated using QIIME pipeline (version 1.9.1).
Statistical analysis
The statistical software JMP version 13 (SAS Institute, Cary, N.C., USA) was used for all statistical analyses. Categorical variables were compared using the chi-squared or Fisher’s exact test, as appropriate. Continuous variables were presented as medians and compared using the Mann–Whitney U test or analysis of variance. Sequence data were presented as median ± standard error of the mean (SEM). P values <0.05 were considered to indicate statistical significance.