Various studies have shown the interplay between the intestinal microbiome, environmental factors, and genetic changes in colorectal cancer (CRC) development. In this review, we highlight the various gut and oral microbiota associated with CRC and colorectal adenomas, and their proposed molecular mechanisms in relation to the processes of “the hallmarks of cancer”, and differences in microbial diversity and abundance between race/ethnicity. Patients with CRC showed increased levels of
Bacteroides, Prevotella, Escherichia coli,
enterotoxigenic
Bacteroides fragilis, Streptococcus gallolyticus, Enterococcus faecalis, Fusobacterium nucleatum
(
F. nucleatum
) and
Clostridium difficile
. Higher levels of
Bacteroides
have been found in African American (AA) compared to Caucasian American (CA) patients. Pro-inflammatory bacteria such as
F. nucleatum
and
Enterobacter
species were significantly higher in AAs. Also, AA patients have been shown to have decreased microbial diversity compared to CA patients. Some studies have shown that using microbiome profiles in conjunction with certain risk factors such as age, race and body mass index may help predict healthy colon
vs
one with adenomas or carcinomas. Periodontitis is one of the most common bacterial infections in humans and is more prevalent in Non-Hispanic-Blacks as compared to Non-Hispanic Whites. This condition causes increased systemic inflammation, immune dysregulation, gut microbiota dysbiosis and thereby possibly influencing colorectal carcinogenesis. Periodontal-associated bacteria such as
Fusobacterium, Prevotella
,
Bacteroides
and
Porphyromonas
have been found in CRC tissues and in feces of CRC patients. Therefore, a deeper understanding of the association between oral and gastrointestinal bacterial profile, in addition to identifying prevalent bacteria in patients with CRC and the differences observed in ethnicity/race, may play a pivotal role in predicting incidence, prognosis, and lead to the development of new treatments.