Presentation on Etiological factors and Laboratory Diagnosis of Meningitis

Objective 1:

• To list the important causative agents of meningitis.

TYPES OF MENINGITIS

• Acute Pyogenic Meningitis
• Aseptic Meningitis
• Chronic Meningitis
  • Tuberculous
  • Fungal
  • Syphillitic
  • Protozoal
  • Helminthe

Causative agents of acute pyogenic meningitis

• Neonates
– Escherichia coli
– Group B streptococci
– Listeria monocytogenes
– Streptococcus pneumoniae

• Children
– Neisseria meningitidis
– Streptococcus pneumoniae,
– Haemophilus influenzae

• Adults
– Streptococcus pneumoniae,
– Neisseria meningitidis

• Elderly
– Listeria species

Causative Agents of Aseptic meningitis

• Common:
- Enteroviruses
- Herpes simplex virus 2 (HSV 2)
- Arthropod borne viruses (Tickborne, West Nile, Murray Valley, Japanese B)
- HIV (Human Immunodeficiency Virus)

• Less common
- Varicella zoster virus (VZV)
- Epstein Barr virus (EBV)

Causative Agents of Chronic Meningitis

Tuberculous meningitis

• Mycobacterium tuberculosis

Syphillitic meningits

• Treponema pallidum

Fungal meningitis

• Cryptococcus neoformans (most common in HIV patients)
• Candida albicans
• Mucor species
• Aspergillus fumigatus
• Coccidioides immitis
• Histoplasma capsulatum
• Blastomyces dermatitidis

Protozoal

• Toxoplasma gondii
• Trypanosoma
• Acanthamoeba

Helminthes

• Taenia solium

Objective 2:

• To outline laboratory diagnosis of bacterial meningitis.

Specimens

• CSF
• Blood
• Sample
• Nasal swab
• Peticheal lesions
• Autopsy

A. Examination of CSF

Macroscopy
• CSF is cloudy under increased pressure and blood may be seen.

CSF is centrifuged and following methods are used:

• Microscopy
• Culture

Microscopy

Unstained preparations: wet mounts

Stained smears:

• Common stains: Gram stain, Ziehl-Neelsen stain
• Fluorescent dyes: Acridine orange, Auramine rhodamine

Gram stain (left) and ZN stain (right)

Culture

Culture Media

• Enriched solid media- blood agar, chocolate agar
• Selective solid medium- MacConkey agar
• Robertson Cooked meat broth (for anaerobes)

Steps:

• CSF inoculated in culture media
• incubation at 35-36°C under 5-10% CO2
• Colonies appear after 18-24 hours, identified by morphology and biochemical reactions.

B. Blood culture

• incubated for 4-7 days, with daily subcultures

C. Nasopharyngeal Swab

• Useful for detection of carriers
• Done without contamination with saliva

D. Petechial lesions

Menigococci may be demonstrated by microscopy and culture

E. Autopsy

• Specimen from meninges, lateral ventricles, or surface of brain and spinal cord
• Within 12 hours of death of patient
• Smear or culture

Biochemical tests

• Catalase test
• Oxidase test
• Indole test
• Urease test
• Coagulase test
• Citrate Utilization test
• Triple sugar iron agar

Agglutination test:

• Direct slide agglutination test with specific antisera
• Latex agglutination test
• Immunoflourescence test
• Other rapid identification methods
• Molecular diagnosis – PCR test

Various changes in Acute Pyogenic Meningitis:

References:

• Textbook of Microbiology
• Diagnostic Microbiology

Prepared and Presented for Correlation Seminar in Kist Medical College by:

Tags: csf analysis, kernig sign, meningitis, neck rigidity, sepsis

Last updated: August 28, 2010

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