Association of colon cancer and saliva microbiome

Aim: The aim of this study was to examine the presence and amount of Fusobacterium nucleatum (Fn), Porphyromonas gingivalis (Pg) and Streptococcus gallolyticus subspecies gallolyticus (Sg) in saliva samples of colorectal cancer (CRC) patients in comparison with healthy controls. Material and Method: Patients with newly diagnosed CRC who have not yet received any treatment were included in the study. Control group consisted of individuals over 50 years of age without a prior diagnosis of malignancy. Polymerase chain reaction (PCR) analyzes were performed with 16S rRNA for identification and quantification of Fn, Sg and Pg strains. Bacterial quantities were reported in log10 copies/ml saliva units. Results: A total of 148 subjects including 71 patients and 77 controls were included in the study. The total amount of bacteria in the saliva samples from the patient and control group were similar (7,51±0,50 vs 7,45±0,62 log10 copies/ml, p=0,549). Detection rates of Fn (97,2% vs 96,1% p>0,99), Sg (31% vs 27,3% p=0,619) and Pg (76,1% vs 75,3% p=0,917) were similar in two groups. Mean Fn amount was higher in patient saliva samples compared with controls (6,89±1,07 vs 6,35±0,78 log10 copies/ml, p=0,001). Mean Sg amount was higher in patient saliva samples (4,12±0,99 vs 3,15±0,58 log10 copies/ml, p<0,001). Saliva Pg amount was similar in two groups. The frequency and amount of Fn, Sg, and Pg were similar in the comparison of tumor localization (right vs left colon) and stage (stage 1-2-3 vs stage 4). Fusobacterium nucleatum and Streptococcus gallolyticus subspecies gallolyticus were found to be significantly lower in the microsatellite insability (MSI) (+) group than in the MSI (-) group [6,15 (4,35-7,96) vs 7,03 (5,18-8,97) log10 copies/ml p=0,036 for Fn; 3,44 (3,18-3,92) vs 4,13 (3,48-7,44) log10 copies/ml, p=0,022 for Sg, respectively]. Evaluation of the salivary Sg amount by ROC curve analysis found to have diagnostic value for CRC (AUC: 0,84 %95 GA 0,72-0,96 p<0,001). Quantity of Sg above 3,32 log10 copy/ml was the best predictor cutoff value for CRC with 82% sensitivity and 76% specificity. Conclusion: In this study, the salivary samples of colorectal cancer patients had higher amounts of Fn and Sg than the control group. This finding may be important for etiopathogenesis of CRC, identification of high-risk groups for CRC, screening of CRC and studies of oral and gingival health for CRC prevention.