Potassium tellurite is primarily used in microbiology as a selective agent in culture media to isolate and identify certain bacteria, particularly Corynebacterium species. It inhibits the growth of many microorganisms, allowing for the differentiation of tellurite-resistant bacteria, which can reduce tellurite to tellurium, forming black colonies. This property is especially useful in diagnosing diphtheria, where Corynebacterium diphtheriae is identified by its ability to grow in the presence of potassium tellurite. Additionally, it is employed in biochemical research to study bacterial metabolism and resistance mechanisms. In industrial applications, potassium tellurite is sometimes used in the production of specialized glass and ceramics, where it imparts unique optical properties.