CNS Infection - Bacterial Identification

Laboratory testing algorithm for Neisseria meningitidis, Streptococcus pneumoniae (pneumococcus), Listeria monocytogenes, Hemophilus influenzae, E. coli, Group B Streptococcus, Staphylococcus aureus, and Pseudomonas aeruginosa

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CNS infectious organisms most often arrive via the bloodstream. The original portal of infection is often the respiratory tract. Alternatively the route of infection may be from sinuses, starting with otitis media, spreading to mastoid air cells, and then to the intracranial cavity. There can be inoculation via direct trauma when the skull is fractured.

The most common organism producing meningitis is a bacterium. Listed above are the most commonly encountered species. However, vaccines available for strains of Hemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis have altered the frequency with which such cases occur. The classic gross and microscopic findings are similar to exudative processes elsewhere caused by bacterial organisms, eliciting a predominantly acute neutrophilic inflammatory response.

The classic findings on examination of CSF include an increased number of WBCs (predominantly polymorphonuclear), low glucose, and elevated protein. The CSF opening pressure is elevated.

The list of organisms is the same across the life span, and the rank order can change by age and location.