This is two overlayed fluorescent microscopy images of Streptococcus mutans, the primary bacteria responsible for dental cavities. When S. mutans forms biofilms on the tooth surface, it produces organic acids as metabolic byproducts that dissolve tooth enamel. The green fluorescent image shows S. mutans biofilm mass when grown in the presence of sucrose, a substrate necessary for substantial bacterial attachment and biofilm formation. The red fluorescent image overlayed depicts S. mutans biofilm mass in the presence of sucrose and purified human salivary mucins. Mucins are key structural components of mucus and saliva that play an important role in host defense.