TAILIEUCHUNG - Chapter 136. Meningococcal Infections (Part 3)

Outer-Membrane Components Associated with Virulence Meningococcal strains are characterized by the expression of capsular polysaccharide and other outer-membrane structures, including LOS (endotoxin). Outer-membrane blebbing, meningococcal autolysis, molecular mimicry, genome plasticity, horizontal DNA exchange, and phase and/or antigenic variation are all important in meningococcal virulence. Capsule The polysaccharide capsule is a major—if not the major—virulence factor of N. meningitidis. As stated above, meningococci isolated from the blood or cerebrospinal fluid (CSF) of patients with invasive meningococcal disease most often express capsules of serogroups A, B, C, Y, and W-135. Isolates from asymptomatic nasopharyngeal carriers are nongroupable or express B, Y, X, Z,. | Chapter 136. Meningococcal Infections Part 3 Outer-Membrane Components Associated with Virulence Meningococcal strains are characterized by the expression of capsular polysaccharide and other outer-membrane structures including LOS endotoxin . Outer-membrane blebbing meningococcal autolysis molecular mimicry genome plasticity horizontal DNA exchange and phase and or antigenic variation are all important in meningococcal virulence. Capsule The polysaccharide capsule is a major if not the major virulence factor of N. meningitidis. As stated above meningococci isolated from the blood or cerebrospinal fluid CSF of patients with invasive meningococcal disease most often express capsules of serogroups A B C Y and W-135. Isolates from asymptomatic nasopharyngeal carriers are nongroupable or express B Y X Z or 29E capsular serogroups. Capsules impart antiphagocytic and antibactericidal properties to the meningococcus and thus enhance meningococcal survival during invasion of the bloodstream or CSF. Capsules also provide protective properties . preventing desiccation and phagocytic killing and antiadherent properties these properties promote meningococcal transmission spread and survival externally and within intracellular compartments such as phagocytic vacuoles. Except in serogroup A the major meningococcal capsular polysaccharides associated with invasive disease are composed of polymers of sialic acid A-acetyl neuraminic acid NANA derivatives. The serogroup B capsule is composed of a2 8 -linked NANA the serogroup C capsule of a-2A9 -linked NANA the serogroup Y capsule of alternating D-glucose and NANA and the serogroup W-135 capsule of D-galactose and NANA. The differences in sialic acid capsule composition are derived from the distinct polysialyltransferases encoded by the fourth gene of the capsule biosynthesis operon which is also used as a basis for capsule-specific PCR diagnosis. A four-gene operon encoding the capsule transport apparatus ctr is conserved among

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