A signature of and depletion, and a link with bacterial glutamate degradation in the Kenyan colorectal cancer patients.

Background: Colorectal cancer (CRC) is the fifth most diagnosed cancer in Sub-Saharan Africa. In Kenya, CRC incidence rates tripled from 1997 to 2017. In the Moi Teaching and Referral Hospital, Moi University, there has been an increase in CRC cases, notably for younger patients. A suggested pathobiology for this increase is gut microbiome dysbiosis. Since, for the Kenyan CRC patient population, microbiome studies are rare, there is a need for a better understanding of how microbiome dysbiosis influences CRC epidemiology in Kenya. In this single-center study, the focus was on profiling the gut microbiome of Kenyan CRC patients and healthy volunteers and evaluating associations between microbiome profiles and the age of CRC patients.

Methods: The gut mucosa-associated microbiome of 18 CRC patients and 18 healthy controls were determined by 16S rRNA sequencing and analyzed for alpha and beta diversity, differential abundance, and microbial metabolic profiling.

Results: Alpha diversity metrics showed no significant differences, but beta diversity metrics showed dissimilarities in the microbial communities between CRC patients and healthy controls. The most underrepresented species in the CRC group were () and (), although () and were overrepresented (linear discriminant analysis, LDA score >2, P<0.05). Also, for CRC patients, significant metagenomic functional alterations were evident in microbial glutamate metabolic pathways (L-glutamate degradation VIII was enriched, and L-glutamate and L-glutamine biosynthesis were diminished) (P<0.05, log2 Fold Change >1). Moreover, the microbiome composition was different for patients under 40 years of age compared to older patients (LDA score >2, P<0.05).

Conclusions: Microbiome and microbial metabolic profiles of CRC patients are different from those of healthy individuals. CRC microbiome dysbiosis, particularly and depletion and glutamate metabolic alterations, are evident in Kenyan CRC patients.