Neisseria spp: Neisseria meningitidis

Neisseria spp: N. meningitidis

• Gram-negative diplococci
° kidney or bean shaped
• Capsulated
• Possess pili
Medically important species
• N. meningitidis (cause meningitis)
• N. gonorrhoeae (cause gonorrhoea)

Cultural characteristics
• Aerobic; require 5-7% CO2 and moisture
• Only grow on enriched media –
° blood and chocolate agar:
• Oxidase positive
• N. gonorrhoeae : ferment glucose
• N. meningitidis : ferment glucose and maltose

N. meningitidis

Antigenic structure and grouping
• Thirteen groups (A,B,C,D,E,H,I,K,L W135. X,Y,Z) on the basis of polysaccharide capsular antigen
• Groups A, B & C are responsible for epidemics of meningitis
• Polysaccharides of groups A,C,W135 are immunogenic – used as vaccines
• Group B is not immunogenic.

Pathogenesis
• Cause disease in human only
• 5-10% of healthy adults and children are carriers (nasopharynx)
• Cause acute bacterial meningitis
Virulence Factors
• Pili help in attachment
• Capsule – antiphagocytic

Meningococcal meningitis
Clinical features
• Fever, headache, vomiting
• Neck stiffness
• Skin petichiae (diffuse rash due to meningococcemia)
• Fulminant DIC - bilateral destruction of adrenal glands (Waterhouse – Friderichsen Syndrome) & shock
Age incidence
• 2/3rd cases in first 5 years of life
• Highest incidence 6-12 months of age (maternal antibodies disappear and naturally acquired antibodies did not appear).

Lab identification of meningococcus
Specimens : CSF & blood
CSF examination
• Turbid CSF due to large no. of neutrophils
Direct Gram-smear
• Intracellular & extracellular Gram-negative diplococci
Culture : Chocolate agar (in 5-10% CO2) :
Blood culture
• Particularly in infants
Direct Serodiagnosis in CSF
° Oxidase Test (positive)
° Ferment glucose and maltose
° Serogrouping

Treatment
• Penicillin is drug of choice :
° penetrates well in inflammed meninges
• In penicillin hypersensitivity
° Ceftriaxone
° Effective against other two pathogens also i.e
H. influenzae & S. pneumoniae
At the end of therapy with penicillin (in adults)
• Give ciprofloxacin to eradicate meningococci because penicillin does not eradicate from nasopharynx: otherwise patient will become a carrier

Epidemiology
• 50% cases are caused by serogroup B
• 20-25% serogroup C
• Others by A,Y, W135
• High incidence in overcrowded areas :
° Military camps & Hajj

Source of infection
• Carriers

Transmission
• Respiratory droplets to close contacts
Prevention
1. Treatment of carriers
• Rifampicin / ciprofloxacin
• Penicillin does not eradicate carrier state
° Due to inadequate penetration of uninflammed sopharyngeal mucosa
° Poor secretion in saliva
2. Chemoprophylaxis to close contacts
• Ciprofloxacin
3. Meningococcal vaccine
• Divalent (gp A & C) &
• Quadrivalent (A,C,Y, W135)
• Not available against group B (not immunogenic)
Given to:
° Military camps and pilgrims
° During epidemic