Virulence factors produced by Neisseria meningitidis and their roles in pathogenesis

Capsular polysaccharides: Neisseria meningitidis strains are frequently encapsulated and 13 different capsular serogroups have been found so far. These capsular polysaccharides protect the meningococci from the action of phagocytic cells and enhance organism’s survival during bloodstream and Central Nervous system invasion.

Meningococcal capsular polysaccharides do not mediate adherence to epithelial cells, and encapsulated cells adhere to mucosal cells less readily than nonencapsulated cells.

IgA1 protease: All meningococci produce IgA1 protease which serves as a virulence factor by abrogating mucosal immunity.  During meningococcal disease and also in asymptomatic nasopharyngeal carriage state, antibodies against IgA1 protease are produced and are detectable.

Plasmids:  Although, Neisseria meningitidis have been found containing tetracycline-resistant plasmids, plasmids are not common in Neisseria meningitidi. Meningococci contaiing Beta-lactamase gene have been found and was found that the plasmid it carries is virtually identical with those of Neisseria gonorrhoeae.

Fimbriae (Pili): Neisseria meningitidis is a piliated organism; the pili mediate attachment of the organism to the mucosal cells of the nasopharynx. It is still not known, whether the pili play a role in the ability of meningococci to cross the blood-brain barrier or to interact with meningeal tissues.

Lipooligosaccharides:  Neisseria meningitids contains Lipooligosaccharides, but it lacks the repeating O antigens. Lipooligosaccharide is found containing carbohydrate lacto-N-neotetrose, which is one of the established meningococcal virulence determinants. Meningococcal Lipooligosaccharide also stimulates release of TNF-alpha, which results in host cell damage.

PorA and PorB proteins: These are the outermembrane proteins of Neisseria meningitidis. It has been proved that porB proteins can insert themselves into membrane of target cells and phagolysosomes and induce apoptosis, thereby facilitating infection and invasion of the host.

Surface proteins of Neisseria meningitidis. Source:
Surface proteins of Neisseria meningitidis. Source:

Opa and Opc proteins: These proteins facilitate bacterial adherence to epithelial cells and neutrophils. Types of opa proteins expressed differ between isolates of different anatomic sites.  Opc proteins functions in mucosal adherence and invasion of endothelial cells. Opc protein is also a target of bactericidal antibodies.

Iron-Binding/Acquisition proteins: These are the integral membrane proteins of Neisseria meningitidis. They help in the acquisition of iron from human transferrin, lactoferrin, and hemoglobin/hepatoglobins.

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