| Microscopically, a gram stain reveals gram negative diplococci within a neutrophil, typical for Neisseria meningitidis. Gram stain and culture can be performed on cerebrospinal fluid obtained via lumbar puncture. A variety of bacteria can cause meningitis, but several are more common, and have an incidence more frequent at certain ages: |
| ORGANISM | PEAK AGE INCIDENCE | GRAM STAIN |
|---|---|---|
| Escherichia coli | Neonates | Gram negative rods |
| Hemophilus influenzae | Infants and Children | Gram negative coccobacilli |
| Neisseria meningitidis | Adolescents and Young adults | Gram negative diplococci |
| Streptococcus pneumoniae | Older adults or Children | Gram positive cocci in chains |
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