Novel two-stage expansion of Streptococcus mutans biofilm supports EPS-targeted prevention strategies for early childhood caries

Early childhood caries (ECC) affects nearly half of preschool children worldwide and characterized by rapid progression across multiple teeth. While Streptococcus mutans (S. mutans) is a keystone species in dental caries, its process for rapid biofilm expansion remains unclear. Using an air-solid interface model simulating the oral environment, we uncovered a novel expansion for S. mutans biofilms. Our findings reveal that S. mutans employs a distinct two-step expansion strategy. Through osmotic pressure, extracellular polymeric substances (EPS) spread and transport bacterial clusters to new sites. Subsequently, the hydroxyapatite surface enables new colony formation. Hydroxyapatite's acid-neutralization properties appear critical for bacterial growth and colonization. Despite successful EPS spreading, environments without hydroxyapatite failed to support new colony formation. These results reveal the unique pattern of rapid ECC progression in sugar-rich environments and establish EPS as a promising therapeutic target, advancing understanding of cariogenic biofilm behavior and preventative strategies for ECC prevention.