Bacterial Meningitis Overview

Bacterial meningitis is an infection of the membranes surrounding the brain and spinal cord.
Common causes include Streptococcus pneumoniae, Neisseria meningitidis (meningococcus), Haemophilus influenzae type b (Hib), and Listeria monocytogenes.
Hib was a common cause of meningitis in children, especially young ones.
Listeria monocytogenes can affect older adults, pregnant women, or people with weakened immune systems.
Other bacteria, including Staphylococcus aureus, streptococci, and pseudomonas, can also cause meningitis.
Spirochetes are another possible bacterial cause.

Morphology: Small, gram-negative diplococci, typically arranged in pairs with flattened sides.
Common cause (second only to Streptococcus pneumoniae) of community-acquired meningitis in healthy adults.
Disease transmission is person-to-person via aerosolization of respiratory tract secretions in crowded areas.
The nasopharynx is the primary site for meningococci colonisation.
Individuals can transmit infection without showing symptoms (carriers).

Pili-mediated colonization of the nasopharynx
Antiphagocytic polysaccharide capsule facilitating spread without specific immunity.
Lipooligosaccharide (a component of the bacterial outer membrane)
IgA proteases, which break down antibodies

Meningococci are encapsulated, unlike other Neisseria.
Classified into serogroups based on capsular polysaccharide antigens.
Important serogroups include A, B, C, Y, and W135; these account for about 90% of infections.
Serogroup A is frequently associated with epidemics.

Incubation period of two to three days before onset.
Sudden onset characterized by severe headache, fever, neck stiffness, and skin rash.
Severe hemorrhagic sepsis may develop.
Types of meningococcal disease include epidemic cerebrospinal meningitis and meningococcal septicaemia.

Examination of cerebrospinal fluid (CSF) for cocci; the fluid typically is under pressure and turbid (cloudy) and high in pus cells
Gram staining of CSF reveals the bacterium inside white blood cells.
Inoculation of the second portion of CSF onto media like blood agar, chocolate agar, or Thayer-Martin medium, incubated in CO2-enriched conditions, following 18 - 24 hours; results in the identification of bacteria by morphology and biochemical reactions
Positive tests for catalase and oxidase
Acid production from glucose and maltose
Blood cultures are often positive in cases of meningococcema and early meningitis (in the 4 to 7 days).
Additional methods include:
- Nasopharyngeal swab (detection of carriers)
- Observation of petechial lesions
- Molecular diagnosis via PCR amplification of meningococcal DNA in CSF or blood

Intravenous penicillin G is often a first-line treatment.
Other third-generation cephalosporins (e.g., cefotaxime or ceftriaxone) or chloramphenicol may be used, depending on sensitivity.
Treatment choice is adjusted based on antimicrobial susceptibility testing.
Vancomycin may be used for penicillin-resistant strains.
Cephalosporins and erythromycin may be used in those allergic to penicillin.

Endogenous spread often begins in the nasopharynx/oropharynx and spreads in distal tissues via the blood or lungs/sinuses/ears/blood/meninges
Frequently a secondary infection, following the flu.
Young children and elderly are most at risk for meningitis.
Five to 75% of the population carry the bacteria.

Polysaccharide capsule: Inhibits phagocytosis.
Pneumolysin: Membrane-damaging toxin that has cytotoxic and complement-activating properties.
IgA protease: Breaks down IgA antibodies.
Autolysin: Causes the lysis of pneumococci.

Using samples like sputum, CSF, blood, and synovial fluid.
Microscopy reveals gram-positive, lanceolate-shaped diplococci with numerous pus cells.
Quellung reaction identifies capsular swelling using type-specific antiserum and methylene blue solution.
Antigen detection uses passive latex agglutination or ELISA.
Culture on blood agar at 37°C in 5% CO2.
Microscopy using Gram’s stain.
Testing for solubility in bile
Optochin sensitivity
Biochemical reactions (ferment Inulin)

Pneumococcal Conjugate Vaccine (PCV13 or Prevnar 13®) (recommended doses for children < 2, 4, 6, 18 months of age)
Pneumococcal Polysaccharide Vaccine (PPSV23 or Pneumovax23®) (for adults > 65 or those with certain medical conditions/smokers)
Chemoprophylaxis of close contacts with rifampin.

Preschool children, who may exhibit pyogenic meningitis, acute epiglottitis, septicemia, facial cellulitis, or osteomyelitis.
Usually a commensal in nasopharyn; may cause otitis media, sinusitis, and chest infections in patients with obstructive airways disease in adults

Gram staining reveals gram-negative, pleomorphic coccobacilli.
Biochemical reactions such as positive tests for oxidase and catalase
Requires factors V (NAD+) and X (hematin) for growth
Most strains does not grow on 5% Sheep Blood Agar; Growth on Chocolate agar;
Some strains may display satellite growth around colonies of Staphylococcus aureus (due to production of NAD by Staphylococci).
Antigen detection using direct and indirect immunofluorescence; Multiplex nucleic acid amplification tests (NAATs).

Ampicillin, chloramphenicol, or third-generation cephalosporins (e.g., ceftriaxone or cefotaxime)
Treatment usually spans 10 days.
If Beta-lactamase is detected, Ceftriaxone is the treatment of choice.
Hib conjugate vaccine is recommended for children under 5.
Vaccination protects against Hib type b meningitis, epiglottitis and other infections.
Infants receive 2, 4, and 6 month vaccinations.
Booster dose given 15 to 18 months post initial infection.

TBM is the most common form of CNS tuberculosis; often fatal, due to its high morbidity/mortality.
Typically a subacute disease; symptoms can persist for weeks before diagnosis.
Cerebrospinal fluid (CSF) analysis often reveals a high number of lymphocytes, elevated protein levels, and low glucose levels.
CSF acid-fast smear and culture may help diagnosis.
Nucleic acid amplification tests (PCR) applied to CSF can be highly specific.

Empiric treatment incorporating first-line drugs, including isoniazid, rifampin, pyrazinamide, and either streptomycin or ethambutol, should be initiated promptly given suspected diagnosis.
Adjunctive treatment with corticosteroids can improve mortality rate.