BLIS K12 and M18 are patented strains of beneficial oral bacteria. They have undergone numerous clinical studies to back up their effectiveness in restoring a healthier oral cavity as well as in reducing various ear-nose-throat infections. The BLIS stands for Bacteriocin Like Inhibitory Substances. A bacteriocin is a toxic substance produced by one strain of bacteria that inhibits, or even kills, off another strain of bacteria. It is similar to an antibiotic but it is narrowly targeted to specific other bacteria (antibiotics target more broadly) and it is a naturally produced substance. Bottom line, BLIS K12 and M18 work to naturally inhibit specific bad bacteria in your mouth.