S-strain bacteria or virulent bacteria are capsulated, made of polysaccharides and amino acids. It is tough and thick mucilage covering, providing protection to bacteria against host immune system. Related Theory The encapsulation makes bacteria more pathogenic. It protects bacteria from phagocytosis by macrophages. Capsule increases tolerance from desiccation. It helps bacteria adhere to surfaces. So capsule is the major determinant of virulence.