The cell wall of pathogenic meningococci contains a toxic LPS or endotoxin. The meningococcal endotoxin is chemically identical to the endotoxin of enteric bacilli.
Depending on group-specific capsular polysaccharide anti-gens, meningococci are subdivided into 13 serogroups (A, B, C, D, X, Y, Z, W135, 29E, H, I, K, and L).
· Meningococci belonging to group A, B, and C are responsible for most of the epidemics and outbreaks of meningitis.
· Group Y and group W135 meningococci cause disease more commonly than groups X and Z.
· Meningococci that lack group-specific antigens are consid-ered nonpathogenic.
Each serogroup includes many serotypes. The classification of the isolates of meningococcal serogroups into their serotypes is based on the differences in the proteins in the outer membrane and in the oligosaccharide part of LOS. For example, Group A meningococci has a single serotype, whereas group B and C meningococci consist of many serotypes. Serotyping of strains is useful for the identification of virulent strains for epidemio-logical studies.