An oral rinse containing brilacidin, a defensin mimetic, with potential antimicrobial and anti-mucositic activities. Upon rinsing with the brilacidin oral rinse, brilacidin imitates defensin as a human host defense protein (HDP), and binds to and disrupts the bacterial cell membrane. This causes bacterial cell membrane lysis and leakage of cellular cytoplasmic contents. This inhibits bacterial activity and may prevent or treat radiation-induced mucositis. Defensins, a family of antimicrobial and cytotoxic peptides expressed mainly by epithelial cells and neutrophils, play a key role in the natural human innate immunity against pathogens.