Bacterial capsules: from a chemical standpoint, capsules are typically composed of which class of macromolecules?

Introduction / Context:
Capsules (a form of glycocalyx) are surface layers that protect bacteria against phagocytosis, desiccation, and environmental stress. Their chemistry influences virulence, immunogenicity, and vaccine design.

Given Data / Assumptions:

• We are to identify the typical chemical nature of capsules.
• Many classic capsules are polysaccharides, but some notable exceptions exist.

Concept / Approach:
Most bacterial capsules are composed of polysaccharides (for example, Streptococcus pneumoniae). However, certain species (notably Bacillus anthracis) produce a polypeptide capsule (poly-D-glutamic acid). Therefore, capsules may be polysaccharide or polypeptide, making the inclusive choice correct.

Step-by-Step Solution:

Verification / Alternative check:
Immunology and microbiology texts list multiple serotypes of polysaccharide capsules used to formulate conjugate vaccines; B. anthracis is the principal example of a polypeptide capsule.

Why Other Options Are Wrong:

• Polypeptide or polysaccharide alone: each is incomplete because both occur.
• None of these: incorrect; capsules are well characterized biopolymers.

Common Pitfalls:
Assuming all capsules are sugars; always remember the poly-D-glutamate capsule exception.

Final Answer:
either (a) or (b)