Researchers in Ireland have turned their attention to the oral microbiome to shed light on colorectal cancer and improve screening programs for the cancer.

The team from University College Cork found that several microbes normally associated with the oral cavity were abundant in CRC compared to controls, and that profiling oral microbiota may serve as an alternative screen for detecting CRC and polyps with better sensitivity than current diagnostic tests.

The results published in Gut also suggest that certain microbiota might help protect against CRC.

The researchers profiled the microbiota in oral swabs, colonic mucosal tissue and faeces from people with CRC, colorectal polyps or controls, and showed that an oral microbiota-based classifier distinguished people with CRC or polyps from healthy controls.

When they combined data from faecal microbiota and oral swab microbiota it increased the discriminatory power, particularly for adenomas which was higher than for tests used currently.

According to the team led by Burkhardt Flemer from the School of Microbiology and APC Microbiome Institute, this suggests that the inclusion of oral microbiota information has the potential to significantly enhance the performance of current diagnostic tests, providing the results can be verified in larger study groups.

“Particularly promising is the high sensitivity for the detection of adenomas (88%) because of the prognostic and therapeutic importance of early discovery of colonic disease,” they report.

The study also found similar networks of oral bacteria at both oral and colonic mucosal surfaces in people with colonic lesions. While these bacteria were more abundant on and off colorectal tumours as well as on and off colorectal polyps, they were also detected in healthy controls, and have been found to be associated with distinct mucosal gene expression profiles, suggesting a role in the development or progression of CRC.

While there was no evidence of direct link between oral and colonic microbiota, in so much as high levels of bacteria in the oral cavity predicting colonic colonisation by the same taxa, the presence and abundance of oral pathogens both in CRC and healthy people was found to be lower if there was an abundance of Lachnospiraceae in the colon.

“A microbiota rich in Lachnospiraceae was negatively correlated with ‘Western diet’ and colonic colonisation with oral bacteria, including oral pathogens associated with CRC, suggesting a protective role, possibly mediated through habitual diet,” the researchers report.

“The concept that the gut microbiota protects against the colonisation of the bowel with environmental bacteria, including pathogens, is well established and, according to our data, is also relevant in the context of CRC…”.