Background: Colon cancer (CRC) is the third most commonly diagnosed malignancy arising mostly from precursors- adenoma and serrated polyp. The relationship between the human gut microbiota and CRC has been identified by different studies; however, its association to the different early precursors of CRC is understudied. Here, we tried to study the relationship between targeted gut bacteria and different colorectal polyp types, location, size and grade of dysplasia.

Material and Methods: Targeted bacteria were detected in 118 colonoscopy- screened adults by surveying 16S rRNA gene of stool samples consisting 31 normal controls, 21 hyperplastic polyp (HP), 16 sessile serrated polyp (SSA), 29 tubular adenoma (TA) and 21 villous/ tubuvillous polyp (VP/ TVP) cases between 2015 and 2017 by absolute quantitative real time PCR technique. The panel of bacteria is including: Streptococcus bovis/gallolyticus, Enterococcus faecalis, Enterotoxigenic Bacteroides fragilis, Fusobacterium nucleatum, Porphyromonas spp, Lactobacillus spp. Roseburia spp. and Bifidobacterium spp.

Results: We observed higher numbers of F.nucleatum, E.feacalis, S.bovis, ENTB and Porphyromonas in tubular and specially in villous/ tubuvillous polyps cases in contrast to samples from normal, HP and SSA groups ( P <0.001 ) Also lower number of Lactobacillus spp. Roseburia spp. and Bifidobacterium spp. were detected in adenomas compared to normal, HP and SSA. In addition we have found significant correlation among selected gut bacterial quantity and the size, location, grade of dysplasia of polyp cases.

Discussion: Our results declared that gut bacteria may contribute in early stages of colorectal carcinogenesis through the development of adenomatous but not SSA. These two polyp types are also different in terms of molecular pathways. Findings may have suggested appropriate bacterial candidates as novel biomarker for adenomatous and CRC early detection.Key words: Fecal Bacteria, sessile serrated polyp, adenomatous polyp, colorectal cancer