Meningitis : Causative Agents and Lab diagnosis

Causative agents of meningitis

Presentation on Etiological factors and Laboratory Diagnosis of Meningitis

Causative agents of meningitis

Objective 1:

  • To list the important causative agents of meningitis.


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

Causative agents of acute pyogenic meningitis

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

Neisseria meningitidis
– Streptococcus pneumoniae,
– Haemophilus influenzae

– Streptococcus pneumoniae,
– Neisseria meningitidis

– Listeria species

Causative Agents of Aseptic meningitis

– 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


• Toxoplasma gondii
• Trypanosoma
• Acanthamoeba


• Taenia solium

Objective 2:

  • To outline laboratory diagnosis of bacterial meningitis.


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

A. Examination of CSF

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

CSF is centrifuged and following methods are used:

  • Microscopy
  • Culture


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 Media

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


  • 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:


  • Textbook of Microbiology
  • Diagnostic Microbiology

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

  • Sharmila Phelu (76)
  • Shradda Shrestha (77)
  • Shuvechha Pandey (78)
  • Srijana Shakya (79)
  • Sulav Shrestha (80)
  • Surakshya Rayamajhi (81)
  • Surendra Pariyar (82)
  • Sushil Dulal (83)
  • Sushmita Sharma (84)
  • Tulsi Ram Shrestha (85)
  • Uday Chandra Prakash (86)
  • Ujjwol Giri (87)
  • Ujwol Karmacharya (88)

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