Microbiome characteristics and Bifidobacterium longum in colorectal cancer patients pre- and post-chemotherapy

Background: With the development of next generation sequencing technology, a lot of research has focused on the role of human microbiome in regulating immunity. The present study evaluated microbiome changes of colorectal cancer patients who received XELOX regimen (capecitabine plus oxaliplatin) without requiring antimicrobials. Methods: Stool samples from 7 patients (3 females/4 males) after screening of 11 patients before and after XELOX chemotherapy were subjected to 16S ribosomal RNA (rRNA) sequencing and flora dynamics compared at baseline and after 8 weeks of chemotherapy. Enrolled patients were newly diagnosed with stage IV colorectal cancer and had not received antimicrobial therapy or surgery. XELOX was administered for 2 cycles or 2-weekly treatments for 3 cycles. Results: The patterns of relative abundance of all bacteria isolated from stool samples before or after chemotherapy treatment appeared to be different, but there were no significant differences in the Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolism pathway between the two groups. The top five pathways in patients were the two-component system, phenylalanine metabolism, degradation of aromatic compounds, beta-lactam resistance and folate biosynthesis. More than 99.6% intestinal flora isolates were bacteria, <0.4% were viruses and Arcbaea. The relative abundances of the 5 most common bacterial phyla in fecal samples before chemotherapy were Bacteroides, Firmicutes, Proteobacteria, Actinobacteria and Verrucomicrobia. The abundance of Actinomycetes in stools after chemotherapy was increased to 2.5 fold higher than before chemotherapy. Bifidobacterium longum species were significantly elevated in stools after chemotherapy (P<0.05), and changes of relative abundance of Bifidobacterium longum species after chemotherapy from baseline in favorable outcome population (stable disease) was significant higher than them in unfavorable outcome population (progressive disease, PD) (P=0.023). Conclusions: The results indicated that Actinornyces in the gut might have a positive clinical outcome for colorectal cancer patients. This idea needs further studies to examine the actions of Actinomytes on inhibition of tumor growth.