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

With the development of next generation sequencing technology, much research has focused on the role of human microbiome in regulating immunity (1,2). Previous studies that involved human and animal models have shown that fluctuations in microbiome levels are associated with the development of various disease states, including metabolic dysfunction, inflammation, infection and cancer (3-7). A number of studies have published their investigations on the risk and clinical outcomes of gastric and colon cancer mediated through the gut microbiome (8-10), and identified various bacterial species that exhibit potential beneficial or pathological effects (11,12). Especially for Actinomyces, a chronic granulomatous disease caused by an anaerobic Gram-positive organism is normally found in the mouth, gut and genitourinary tract, while progressive actinomycosis as well as advancing malignancy may play significant roles in a patient’s demise, although it is a rare but potentially fatal combination of disease and a hitherto undescribed cause of unresectable rectal cancer (13). Breakdown of the mucosal barrier due to trauma (prior to surgery, endoscopic procedures or intestinal perforations, etc.), immunosuppression (steroid therapy, diabetes or tumors) or chronic inflammatory diseases caused by foreign bodies, may be triggered by the penetration of Actinomyces bacteria into the abdomen (14,15). Furthermore, fecal microflora transplantation (FMT) has been shown to reduce the risk of infection in immunocompromised patients (16). However, the optimal composition of microbiota transplants for restoring gut microbiota in colorectal cancer patients undergoing intense anticancer therapies remains uncertain. Furthermore, we are unaware of any study that has closely examined Actinomyces bacteria isolated from the gut microbiota of colorectal cancer patients