ABSTRACTThe gut microbiome is a vast reservoir of microbes, some of which produce antimicrobial peptides called bacteriocins that may inhibit specific bacteria associated with disease. Fusobacterium nucleatumis an emerging human bacterial pathogen associated with gastrointestinal diseases including colorectal cancer (CRC). In this study, fecal samples of healthy donors were screened for potential bacteriocin-producing probiotics with antimicrobial activity against F. nucleatum. A novel isolate, designated as Streptococcus salivariusDPC6993 demonstrated a narrow-spectrum of antimicrobial activity against F. nucleatum in vitro. In silicoanalysis of the S. salivariusDPC6993 genome revealed the presence of genes involved in the production of the bacteriocins salivaricin A5 and salivaricin B. After 6 h in a colon fermentation model, there was a significant drop in the number of F. nucleatumin samples that had been simultaneously inoculated with S. salivariusDPC6993 + F. nucleatumDSM15643 compared to those inoculated with F. nucleatumDSM15643 alone (mean ± SD: 9243.3 ± 3408.4 vs 29688.9 ± 4993.9 copies/μl). Furthermore, 16S rRNA amplicon analysis revealed a significant difference in the mean relative abundances of Fusobacteriumbetween samples inoculated with both S. salivariusDPC6993 and F. nucleatumDSM15643 (0.05%) and F. nucleatumDSM15643 only (0.32%). Diversity analysis indicated minimal impact exerted by S. salivariusDPC6993 on the surrounding microbiota. Overall, this study highlights the ability of a natural gut bacterium to target a bacterial pathogen associated with CRC. The specific targeting of CRC-associated pathogens by biotherapeutics may ultimately reduce the risk of CRC development and positively impact CRC outcomes.