Abstract
The encapsulated bacteria Streptococcus pneumoniae, Neisseria meningitis, Haemophilus influenzae, and Streptococcus agalactiae (Group B Streptococcus) have been responsible for the majority of severe infections in children for decades, specifically bacteremia and meningitis. Isolates which cause invasive disease are usually surrounded by a polysaccharide capsule, which is a major virulence factor and the key antigen in protective protein-polysaccharide conjugate vaccines. Protection against these bacteria is largely mediated via polysaccharide-specific antibody and complement, although the contribution of these and other components, and the precise mechanisms, vary between species and include opsonophagocytosis and complement-dependent bacteriolysis. Further studies are required to more precisely elucidate mechanisms of protection against non-type b H. influenzae and Group B Streptococcus.
Highlights
Encapsulated bacteria have been responsible for the majority of bacteremia and meningitis in children for many decades [1,2,3]
In concurrence with the other encapsulated bacteria, the most important mediator of host defense against H. influenzae type b (Hib; the best studied serotype) is antibody directed against the type b capsular polysaccharide polyribosylribitol phosphate (PRP)
Antigen-specific antibody directed at the capsular polysaccharide clearly has the central role in protection against invasive infection by encapsulated bacteria, in both children and adults
Summary
Encapsulated bacteria have been responsible for the majority of bacteremia and meningitis in children for many decades [1,2,3]. In neonates and young infants, Group B Streptococcus (GBS) is the major cause of bacteremia and meningitis [1] These organisms have the shared characteristic of being surrounded by a polysaccharide capsule, which is a key virulence factor because it helps the bacteria evade complement deposition and subsequent phagocytosis and killing. Asplenic or hyposplenic individuals (e.g., post-splenectomy, sickle cell disease) are rendered at much higher risk of life-threatening infection, reflected by the increased rates of infection by S. pneumoniae in particular— and other encapsulated bacteria such as H. influenzae and N. meningitidis [13,14,15,16,17,18,19] Such individuals are recommended to receive vaccination against all of these three pathogens, even when not in a high risk age group, in addition to long-term antibiotic prophylaxis to prevent infection [19]
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