BACKGROUND Colorectal cancer (CRC) is one of the prevailing causes of cancer mortality in the world. A common screening test for CRC is based on the human hemoglobin immunochemical based fecal occult blood test (iFOBT), which consists in the detection of blood in the patient's stool. In addition to iFOBT, recent studies support the use of the gut microbiome as a biomarker for CRC prediction. However, these studies did not take into account the effect of blood itself on the microbiome composition, independently of CRC. Therefore, we investigated the microbiome of patients undergoing the iFOBT screening in order to determine the effect of blood alone. Our cohort consisted of patients who had no blood in their stools (n = 265) or did have blood but no underlying precancerous or cancerous lesions (n = 235). We also identified bacterial taxa specifically associated with the presence of blood in stools. RESULTS We observed significant differences in the intestinal bacterial composition that could be solely caused by the presence of blood in stools. More precisely, we identified 12 bacterial species showing significant differences in abundance between both our study groups. These species, Bacteroides uniformis, Collinsella aerofaciens, Eggerthella lenta and Clostridium symbiosum demonstrated increased abundance in the presence of blood. In contrast, the species Prevotella copri, Coprococcus eutactus and catus, Faecalibacterium prausnitzii, Roseburia faecis, Blautia obeum, Gemmiger formicilis and Clostridium celatum showed decreased abundance in patients with blood in their stools. Notably, we found multiple taxa that were reported in previous studies linking microbiome composition and diseases. CONCLUSIONS We show that, in the absence of disease, blood in the stools has a major influence on the composition of the microbiome. Our data suggest that blood itself should be taken into consideration when investigating the microbiome signatures of intestinal diseases.

中文翻译：

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血液对人体肠道微生物组的影响。

背景技术结直肠癌（CRC）是世界上癌症死亡的普遍原因之一。CRC的常见筛查测试是基于人类血红蛋白免疫化学的粪便潜血试验（iFOBT），它包括检测患者粪便中的血液。除iFOBT外，最近的研究还支持将肠道微生物组用作CRC预测的生物标记。但是，这些研究没有考虑血液本身对微生物组组成的影响，而与CRC无关。因此，我们调查了进行iFOBT筛查的患者的微生物组，以确定单独血液的作用。我们的研究对象包括大便中无血（n = 265）或有血但无潜在的癌前或癌性病变（n = 235）的患者。我们还确定了与粪便中的血液存在特别相关的细菌类群。结果我们观察到肠道细菌组成的显着差异可能完全由粪便中血液的存在引起。更准确地说，我们确定了12个细菌物种，在两个研究组之间显示出丰度的显着差异。这些物种，即统一的拟杆菌，空气中的Collinsella aerofaciens，Leggerthella lenta和共生梭菌（Clostridium symbiosum）在有血的情况下表现出丰富的增加。相比之下，普雷沃特氏菌，大肠结肠炎球菌和猫属，普氏嗜藻杆菌，玫瑰色玫瑰菌，黑液杆菌，Gemmiger formicilis和Clostridium celatum的粪便中血液含量降低。值得注意的是 我们发现了先前研究中报告的多种分类群，这些分类群将微生物组组成与疾病联系起来。结论我们表明，在没有疾病的情况下，粪便中的血液对微生物组的组成具有重大影响。我们的数据表明，在调查肠道疾病的微生物组特征时应考虑血液本身。