Higher enterococcus counts indicate a lower risk of colorectal adenomas: a prospective cohort study

// Atsuko Kawano 1 , Hideki Ishikawa 2 , Michihiro Mutoh 3 , Hiroyuki Kubota 4 , Kazunori Matsuda 5 , Hirokazu Tsuji 4 , Kazumasa Matsumoto 4 , Koji Nomoto 4 , Ryuichiro Tanaka 4 , Tomiyo Nakamura 6 , Keiji Wakabayashi 7 and Toshiyuki Sakai 2 1 Institute of Gastroenterology, Zenjinkai Shimin-no-Mori Hospital, Miyazaki, Japan 2 Department of Molecular-Targeting Cancer Prevention, Kyoto Prefectural University of Medicine, Kyoto, Japan 3 Epidemiology and Prevention Group, Research Center for Cancer Prevention and Screening, National Cancer Center, Tokyo, Japan 4 Yakult Central Institute, Tokyo, Japan 5 Yakult Honsha European Research Center for Microbiology, ESV, Gent Zwijnaarde, Belgium 6 Faculty of Nutrition, University of Kochi, Kochi, Japan 7 Graduate Division of Nutritional and Environmental Sciences, University of Shizuoka, Shizuoka, Japan Correspondence to: Michihiro Mutoh, email: mimutoh@ncc.go.jp Keywords: cancer prevention; colorectal cancer; enterococci; endoscopic polypectomy; intestinal microbiota Received: September 15, 2017      Accepted: March 24, 2018      Published: April 20, 2018 ABSTRACT Intestinal bacteria play an important role in human health. This prospective cohort study aimed to investigate the relationship between the abundance of different intestinal bacteria and the risk of developing colorectal cancer (CRC). Fecal samples from CRC patients ( n =  157) were collected at the start of the study wherein patients subsequently underwent endoscopy to remove polyps. Gut bacteria were isolated by using specific culture methods and the fecal counts of various bacteria were quantified by reverse-transcription-quantitative-PCR (RT-qPCR) assays. The obtained data were subjected to cohort analysis in relation to the incidence of colorectal adenomas after 4 years of intervention. No relationship was detected between the counts of major intestinal bacteria and the incidence of colorectal adenomas. However, interestingly, a significant negative correlation was noted between colorectal adenoma incidence and the counts of bacteria grown on Columbia blood agar base (COBA) ( P =  0.007). The risk ratio of colorectal adenomas was 0.58 (95% CI: 0.35–0.96) in the group with the highest bacterial count compared to the lowest. Bacteria grown on COBA were more abundant in older patients, non-smoking patients, and patients with a lower body mass index. The RT-qPCR results revealed a significantly lower colorectal adenoma incidence in subjects with higher enterococcal count as compared to subjects with a lower count, with a risk ratio of 0.47 (95% CI: 0.30–0.76). Correlation of a higher enterococci count with a lower risk of CRC development suggests that certain Enterococcus strains may have adenoma suppressive effects.