显微镜下，中性粒细胞内可见的革兰氏染色阴性的双球菌，为脑膜炎奈瑟球菌。腰穿抽取脑液可进行革兰氏染色和细菌培养。许多细菌都可能引起脑膜炎，但是几种最常见,并且特定的年龄段发生的机率更大。如大肠杆菌、嗜血流感杆菌、脑膜炎奈瑟菌、肺炎链球菌。
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 |