Microbiology · MU Sofia

107. Microbiological Aspects of Central Nervous System (CNS) Infections

Covers the main CNS infections (meningitis, encephalitis, brain abscess and myelitis), how pathogens reach the nervous system, and the immune and inflammatory response they provoke. Goes on to the typical causative organisms for each condition, their clinical signs, laboratory diagnosis from CSF and blood, empirical and specific treatment, and prevention. Tables summarise pathogens, clinical features and treatments.

Inside: 8 sections · 5 labelled pictures · 3 tables · 16 flashcards · 3 min

Topic 107 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 8 sections, about 225 words (3 min of reading), with 16 flashcards.

In this note

  1. Microbiological Aspects of Central Nervous System (CNS) Infections
  2. I. Overview of CNS Infections
  3. II. Main Types of CNS Infections & Etiology
  4. III. Pathogenesis of CNS Infections
  5. IV. Clinical Features (General Clues)
  6. V. Laboratory Diagnosis
  7. VI. Treatment Overview
  8. VII. Prevention

I. Overview of CNS Infections

  • CNS infections include meningitis, encephalitis, brain abscess, and myelitis.
  • The CNS is normally sterile. Infections are serious due to limited immune surveillance and the blood–brain barrier (BBB).
  • Pathogens reach CNS via:
  • Hematogenous spread
  • Direct extension (e.g., sinusitis, otitis media)
  • Neural pathways (e.g., rabies, HSV)

II. Main Types of CNS Infections & Etiology

A. Meningitis (inflammation of the meninges)

B. Encephalitis (inflammation of brain parenchyma)

  • Viruses are main cause
  • HSV-1 (temporal lobe necrosis), Arboviruses (WNV, JE), Rabies, VZV, CMV (immunocompromised)
  • Rare bacterial causes: Listeria, Mycoplasma

C. Brain Abscess

  • Pyogenic infection with focal pus accumulation
  • Causative agents:
  • Streptococcus spp., Staph. aureus, anaerobes (Bacteroides)
  • Spread from sinusitis, dental infections, otitis
  • In immunocompromised: Toxoplasma gondii

D. Myelitis (spinal cord inflammation)

  • Often viral: Poliovirus, Enteroviruses, West Nile virus

III. Pathogenesis of CNS Infections

  • Entry:
  • Hematogenous: bacteria cross BBB during bacteremia
  • Local spread: mastoiditis → meningitis
  • Neural: rabies via peripheral nerves to CNS
  • Immune response in CNS:
  • Leads to inflammation, edema, elevated ICP
  • In meningitis: increased CSF neutrophils, cytokines, BBB disruption

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