Meningococcemia causes

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Meningococcemia is caused by a bacteria called Neisseria meningitidis. The bacteria frequently lives in a person's upper respiratory tract without causing visible signs of illness. The bacteria can be spread from person to person through respiratory droplets. Family members and those closely exposed to someone with the condition are at increased risk. The infection occurs more frequently in winter and early spring.

Taxonomy

• N. meningitidis is a gram negative bacteria.
• It belongs to phylum proteobacterium from the family of Neisseriaceae.
• It belongs to class beta proteobacterium.
• The order is Neisseriales.
• It belongs to family Neisseriaceae.
• Genus name is Neisseria.
• Species name is N. meningitidis.

Neisseria Meningitidis

• N. meningitidis are gram-negative, coffee-bean shaped diplococci that may occur intracellularly or extracellularly in PMN leukocytes.
• N. meningitidis is a fastidious organism, which grows best at 35-37°C with ~5% CO2 (or in a candle-jar).
• It can grow on both a blood agar plate (BAP) and a chocolate agar plate (CAP).
• Colonies of N. meningitidis are grey and unpigmented on a BAP and appear round, smooth, moist, glistening, and convex, with a clearly defined edge. N. meningitidis appear as large, colorless-to-grey, opaque colonies on a CAP.
• Prior to identification and characterization testing procedures, isolates should always be inspected for purity of growth and a single colony should be re-streaked, when necessary, to obtain a pure culture
• Twelve serogroups, based on the biochemical composition of capsular polysaccharides, are currently recognized: A, B, C, H, I, K, L, W135, X, Y, Z, and 29E (Z').
• Serogroup D is no longer recognized as a serogroup.
• Serogroups A, B, C, W135 and Y are the 5 most common causes of bacterial meningitis.
• Serogroup A has been the most common cause of epidemics in Africa and Asia.
• Serogroups C, W135, and X have also been reported as causes of epidemics in several parts of Africa as well. Serogroup-specific antisera for these major serogroups are available commercially.

Culture: Distinctive clusters of colonies Neisseria Meningitidis

Culture on CAP mediaNeisseria Meningitidis

Genomic sequence

• MC58 (serogroup B), Z2491(serogroup A), FAM18 (serogroup C) have been identified.
• 70% of the genome is core meningococcal genome that accounts for major metabolic process.
• IHT-A1 locus contains genes for synthesizing capsule, and transport of it.

Outer membrane components

• Virulence is determined by capsular polysacchride, outer membrane proteins and lipopolysacchride.
• The epidemics are due to modified expression of this capsule.
• Meningococci that cannot be grouped are usually found in nasopharynx of the contacts.
• Endotoxin is a major component of the outer membrane.