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In this Article, in the section entitled ‘Quantitative real-time PCR’ within the Supplementary Methods, the probe for the Bacteroides fragilis 16S real-time PCR reaction was listed incorrectly as 5ʹHEX-AGGGACTGGAAGGCTTTACTGCTTC-3ʹBHQ1. The correct probe for Bacteroides fragilis 16S should be listed as 5ʹHEX-ACACGTATCCAACCTGCCCTTTACTCG-3ʹBHQ1. The mistake was a result of a copy and paste error with a different primer set targeting a B. fragilis toxin gene. All qPCR reactions were performed using the correct probe, and therefore no data were affected.

Colorectal cancer (CRC) remains the third most common cancer worldwide, with a growing incidence among young adults. Multiple studies have presented associations between the gut microbiome and CRC, suggesting a link with cancer risk. Although CRC microbiome studies continue to profile larger patient cohorts with increasingly economical and rapid DNA sequencing platforms, few common associations with CRC have been identified, in part due to limitations in taxonomic resolution and differences in analysis methodologies. Complementing these taxonomic studies is the newly recognized phenomenon that bacterial organization into biofilm structures in the mucus layer of the gut is a consistent feature of right-sided (proximal), but not left-sided (distal) colorectal cancer. In the present study, we performed 16S rRNA gene amplicon sequencing and biofilm quantification in a new cohort of patients from Malaysia, followed by a meta-analysis of eleven additional publicly available data sets on stool and tissue-based CRC microbiota using Resphera Insight, a high-resolution analytical tool for species-level characterization. Results from the Malaysian cohort and the expanded meta-analysis confirm that CRC tissues are enriched for invasive biofilms (particularly on right-sided tumors), a symbiont with capacity for tumorigenesis (Bacteroides fragilis), and oral pathogens including Fusobacterium nucleatum, Parvimonas micra, and Peptostreptococcus stomatis. Considered in aggregate, species from the Human Oral Microbiome Database are highly enriched in CRC. Although no detected microbial feature was universally present, their substantial overlap and combined prevalence supports a role for the gut microbiota in a significant percentage (>80%) of CRC cases., Bowel cancer: Spotlight of suspicion on bacteria Many studies have found a link between gut microbes and bowel cancer, the third most common cancer worldwide. The details of the association, however, have remained elusive. Researchers in the USA and Malaysia, led by Dr. Cynthia Sears at John Hopkins School of Medicine in Maryland, examined mucosal biofilm status by fluorescence microscopy and performed a meta-analysis of bacterial genetic associations in stool and colon tissues to clarify the connection. They found that bowel cancers were enriched in invasive bacterial biofilms as well as several specific gut and oral species, including one - Fusobacterium nucleatum - known to promote tumorigenesis in mouse models. Analyzing gut microbial populations might help assess bowel cancer risk. Further research is needed, however, to determine if these bacteria directly contribute to disease causality.

Colorectal cancer (CRC) is ranked the third most common cancer in human worldwide. However, the exact mechanisms of CRC are not well established. Furthermore, there may be differences between mechanisms of CRC in the Asian and in the Western populations. In the present study, we utilized a liquid chromatography-mass spectrometry (LC-MS) metabolomic approach supported by the 16S rRNA next-generation sequencing to investigate the functional and taxonomical differences between paired tumor and unaffected (normal) surgical biopsy tissues from 17 Malaysian patients. Metabolomic differences associated with steroid biosynthesis, terpenoid biosynthesis and bile metabolism could be attributed to microbiome differences between normal and tumor sites. The relative abundances of Anaerotruncus, Intestinimonas and Oscillibacter displayed significant relationships with both steroid biosynthesis and terpenoid and triterpenoid biosynthesis pathways. Metabolites involved in serotonergic synapse/ tryptophan metabolism (Serotonin and 5-Hydroxy-3-indoleacetic acid [5-HIAA]) were only detected in normal tissue samples. On the other hand, S-Adenosyl-L-homocysteine (SAH), a metabolite involves in methionine metabolism and methylation, was frequently increased in tumor relative to normal tissues. In conclusion, this study suggests that local microbiome dysbiosis may contribute to functional changes at the cancer sites. Results from the current study also contributed to the list of metabolites that are found to differ between normal and tumor sites in CRC and supported our quest for understanding the mechanisms of carcinogenesis.