Oral Microbiota as Novel Biomarkers for Colorectal Cancer Screening

Simple Summary Colorectal cancer (CRC) is the third most common cancer type worldwide. Increasingly, the gastrointestinal microbiome has been identified as an important factor in the pathogenesis of CRC. In this work, for the first time in Iran, an analysis of the whole microbiome in saliva and stool samples of CRC patients has been conducted, and the results were investigated and compared with healthy controls (HCs). In the present study, we found that there is a distinct clustering of genera associated with the saliva and fecal samples of CRC patients and HCs, respectively, pointing to special microbial signatures in both conditions. However, the roles of microbiota in CRC and HCs require further investigation. Alterations of the gut microbiome in cases of colorectal cancer (CRC) hint at the involvement of host-microbe interactions in the onset and progression of CRC and also, possibly, provide novel ways to detect and prevent CRC early. The aim of the present study was to evaluate whether the oral and fecal microbiomes of an individual can be suitable for CRC screening. Oral and fecal samples (n = 80) were gathered in Taleghani hospital, affiliated with Shahid Beheshti University of Medical Sciences, Tehran-Iran, from CRC stage 0 and I patients and healthy controls (HCs), who were screened for the first time. Microbial metagenomics assays were performed for studying microbiota profiles in all oral and fecal samples gathered. An abundance of top bacterial genera from both types of specimens (fecal and saliva samples) revealed a distinction between CRC patients and HCs. In saliva samples, the alpha diversity index was different between the microbiome of HCs and CRC patients, while beta diversity showed a densely clustered microbiome in the HCs but a more dispersed pattern in CRC cases. The alpha and beta diversity of fecal microbiota between HCs and CRC patients showed no statistically significant differences. Bifidobacterium was identified as a potential bacterial biomarker in CRC saliva samples, while Fusobacterium, Dialister, Catonella, Tennerella, Eubacterium-brachy-group, and Fretibacterium were ideal to distinguish HCs from CRC patients. One of the reasons for the heterogeneity of CRC may be the gastrointestinal (GI) tract microbiota, which can also cause systematic resistance to CRC. Moreover, an evaluation of saliva microbiota might offer a suitable screening test for the early detection of this malignancy, providing more accurate results than its fecal counterpart.