Overview Yersinia pestis Escherichia coli meningeal strains only Salmonella typhi Streptococcus pneumoniae and Streptococcus pyogenes Neisseria meningitidis Klebsiella pneumoniae Haemophilus influenzae type B (B polysaccharide) Pseudomonas aeruginosa Bordetella pertussis and Bacillus anthracis (contains poly D-glutamate capsule) Cryptococcus neoformans only encapsulated fungal pathogen Physiology Quellung reaction antibodies bind to capsule used to visualize S. pneumoniae H. influenzae N. meningitidis K. pneumoniae Capsules serve as antigen in vaccines H. influenzae type B vaccine meningococcal vaccines S. pneumoniae vaccine (pneumovax) Capsules act as antiphagocytic virulence factors Encapsulated bacteria can generally cause meningitis produce IgA protease undergo transformation take up DNA from their environment Opsonization antibodies bind to capsule to aid phagocytosis by macrophages and neutrophils clearance of these pathogens depends on presence of C3 complement or IgG and a functional spleen