Which encapsulated bacteria is noted for having a polypeptide capsule instead of a polysaccharide capsule?

Bacillus anthracis is noted for having a polypeptide capsule made of poly-D-glutamic acid, which is distinct from the more common polysaccharide capsules found in many other bacteria. This unique capsule contributes to the virulence of Bacillus anthracis by inhibiting phagocytosis, allowing the bacteria to evade the immune system and establish an infection. The structure of the capsule plays a crucial role in determining how the bacteria interact with host defenses, specifically by providing a protective layer that impedes the action of immune cells.

In contrast, other bacteria listed have polysaccharide capsules, which are made of long chains of sugar molecules. For instance, Streptococcus pneumoniae and Neisseria meningitidis both possess polysaccharide capsules that are important for their pathogenicity, enabling them to avoid detection and destruction by the host's immune system. Escherichia coli also exhibits polysaccharide capsules, which may vary in composition depending on the strain and can play roles in adherence and virulence.

The distinct composition of the capsule in Bacillus anthracis highlights its unique adaptations for survival and pathogenicity, making it significant in the study of bacterial pathogens.