What are extracellular polymeric substances and what role do they play in oral biofilms?

• A. EPS are extracellular polysaccharides and proteins that form the biofilm matrix, enabling aggregation, protection, and nutrient retention.
• B. EPS are intracellular enzymes that metabolize sugars.
• C. EPS are signaling lipids that attract phagocytes.
• D. EPS are host-derived glycoproteins integrated into biofilm.

Answer: (C)

Extracellular polymeric substances are the matrix that holds a biofilm together. They are secreted by the microbial community and consist mainly of extracellular polysaccharides, along with proteins, extracellular DNA, and some lipids. In the oral environment, this matrix forms the scaffold of dental plaque, enabling cells to stick to each other and to the tooth surface.

The polysaccharide components, such as glucans produced by bacteria like Streptococcus mutans, are especially important for adherence to the tooth and for building a cohesive, three-dimensional structure. The matrix also traps nutrients and enzymes, helping to retain resources close to the community and creating a diffusion barrier that can slow the penetration of antimicrobial agents and immune factors. Extracellular DNA and matrix-associated proteins contribute to the stability and age-related maturation of the biofilm, supporting complex organization and resilience.

These substances are microbial in origin and are extracellular, not intracellular enzymes. They are not signaling lipids that recruit phagocytes, and they are not host-derived glycoproteins forming the biofilm; rather, EPS are secreted by the bacteria and serve as the main physical and chemical framework of the biofilm.