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Chapter 136. Meningococcal Infections

Neisseria meningitidis is the etiologic agent of two life-threatening diseases: meningococcal meningitis and fulminant meningococcemia. More rarely, meningococci cause pneumonia, septic arthritis, pericarditis, urethritis, and conjunctivitis. Most cases are potentially preventable by vaccination. Etiologic Agent Meningococci are gram-negative aerobic diplococci. Unlike the other neisseriae, they have a polysaccharide capsule. They are transmitted among humans—their only known habitat—via respiratory secretions. Colonization of the nasopharynx or pharynx is much more common than invasive disease. Microbiology and Classification On the basis of genome sequencing, N. meningitidis is categorized as a βproteobacterium related to Bordetella, Burkholderia, Kingella, and Methylomonas and—more distantly—to Vibrio, Haemophilus,. | Chapter 136. Meningococcal Infections Neisseria meningitidis is the etiologic agent of two life-threatening diseases meningococcal meningitis and fulminant meningococcemia. More rarely meningococci cause pneumonia septic arthritis pericarditis urethritis and conjunctivitis. Most cases are potentially preventable by vaccination. Etiologic Agent Meningococci are gram-negative aerobic diplococci. Unlike the other neisseriae they have a polysaccharide capsule. They are transmitted among humans their only known habitat via respiratory secretions. Colonization of the nasopharynx or pharynx is much more common than invasive disease. Microbiology and Classification On the basis of genome sequencing N. meningitidis is categorized as a p-proteobacterium related to Bordetella Burkholderia Kingella and Methylomonas and more distantly to Vibrio Haemophilus and Escherichia coli. Meningococci are traditionally classified by serologic typing systems based on structural differences in capsule serogroup major outer-membrane protein OMP porin PorB serotype minor porin PorA serosubtype and lipooligosaccharide LOS immunotype . Thus for example the meningococcal strain designation B 2b P1.5 L3 7 9 reflects the serogroup B serotype 2b serosubtype P1.5 and immunotype L3 7 9 . Meningococci are also differentiated from the other Neisseriaceae by their pattern of sugar fermentation. N. gonorrhoeae ferments only glucose N. meningitidis ferments glucose and maltose and N. lactamica ferments glucose maltose and lactose. Meningococci are classified into serogroups according to the antigenicity of their capsular polysaccharides which reflects structural differences in these carbohydrates. Five serogroups A B C Y and W-135 see below are responsible for 90 of cases of meningococcal disease worldwide. One limitation of serogroup classification based on polysaccharide capsular structure is that the genes for capsule biosynthesis can be transferred from one strain to another with consequent changes in