Capsular Operons

The major factor determining the different pathogenicities of meningococci and their close relatives, the gonococci, is the polysaccharide capsule. The capsule protects meningococci from complement attack and phagocytosis and is indispensable for systemic spread of the bacteria during sepsis and meningitis (1 –5 ). The influence of the capsule on transmission of the bacteria, colonization of the human host, entry into the bloodstream, and passage of the blood-brain barrier (BBB), respectively, is less well-understood. Colonizing meningococci may be acapsular (6 ,7 ), and at least in serogroup B meningococci, there is evidence that transient loss of encapsulation owing to genetic-switching mechanisms facilitates entry into epithelial cells (8 ,9 ). Characterization of meningococcal capsules in disease and carrier isolates is important as part of the meningococcal typing scheme of outbreak isolates. Typing is performed to determine the transmission of index strains. Capsular serogrouping is of particular importance in the assessment of the suitability of vaccination in outbreak management (reviewed in ref . 10 ). This chapter describes serological and molecular techniques used for the determination of serogroups and capsular genotypes.