7 Sept 2026 · Case #002
Listeria monocytogenes meningitis
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Diagnosis
Listeria monocytogenes meningitis
First-line treatment
IV ampicillin (plus gentamicin)
How the diagnosis is reached
Fever, headache, neck stiffness and confusion are bacterial meningitis, but two details move this away from the pneumococcus that would otherwise head the list. The first is the neurology: nystagmus, facial weakness and a wide-based gait are brainstem signs, and a rhombencephalitis layered on meningitis is close to a signature for Listeria, which reaches the brainstem in a way the common pathogens do not. The second is the fluid, lymphocyte-predominant at 62 per cent rather than the near-pure neutrophilia of pneumococcal disease, with gram-positive rods on the stain where one expects gram-positive diplococci. Age over 50, six years of corticosteroids for rheumatoid arthritis, and a diet of soft cheese and deli meats supply both the susceptibility and the source. The treatment point is what makes this case worth knowing. Listeria carries intrinsic resistance to every cephalosporin, a property of its penicillin-binding proteins rather than something acquired, so the standard empiric pairing of ceftriaxone and vancomycin cannot touch it. Her failure to improve on exactly that regimen is the clue demonstrating it. What she needs is high-dose intravenous ampicillin, an aminopenicillin, usually with gentamicin for synergy and for at least three weeks. It is also why ampicillin is added empirically for anyone over 50, pregnant or immunosuppressed, long before an organism is named. Trimethoprim-sulfamethoxazole covers the penicillin-allergic.
Key clinical clues
- Age >50 plus chronic immunosuppression are classic Listeria risk factors
- Dietary exposure to unpasteurized soft cheese and deli meats suggests a foodborne source
- Brainstem signs (nystagmus, facial weakness, ataxia) suggest rhombencephalitis, a hallmark of Listeria CNS infection
- CSF shows Gram-positive rods with a mixed/lymphocytic pleocytosis rather than pure neutrophils
- No improvement on ceftriaxone + vancomycin, standard empiric regimens do not cover Listeria
The case in full
Presenting complaint
Patient history
A 74-year-old woman with rheumatoid arthritis, maintained on long-term low-dose prednisone, is brought in by her family for two days of fever, worsening headache, and confusion. Earlier today she seemed unsteady on her feet.
Neurological examination
Physical examination
She is febrile and lethargic but arousable. She has nuchal rigidity and photophobia. Examination also reveals horizontal nystagmus, mild left-sided facial weakness, and an unsteady, wide-based gait: findings suggesting brainstem involvement rather than the cerebral hemispheres alone.
Vital signs & background
Vital signs
She has no history of recent travel or sick contacts. Her rheumatoid arthritis has required chronic immunosuppression for the past six years, and she also mentions eating soft cheeses and delicatessen meats regularly.
| Parameter | Value | Reference |
|---|---|---|
| Temperature | 38.9 °CRef 36.1–37.5 | 36.1–37.5 |
| Heart rate | 104 bpmRef 60–100 | 60–100 |
| Blood pressure | 128/78 mmHg | – |
Cerebrospinal fluid analysis
Laboratory results
A non-contrast head CT shows no mass effect, so a lumbar puncture is performed.
| Parameter | Value | Reference |
|---|---|---|
| CSF WBC count | 420 cells/µLRef 0–5 | 0–5 |
| CSF differential | 62% lymphocytes, 30% neutrophilsRef Lymphocytes only, no neutrophils | Lymphocytes only, no neutrophils |
| CSF protein | 180 mg/dLRef 15–45 | 15–45 |
| CSF glucose | 28 mg/dLRef 50–80 | 50–80 |
| CSF Gram stain | Gram-positive rodsRef No organisms | No organisms |
CSF culture
Pathology
CSF culture grows small, motile, gram-positive rods that are catalase-positive and show a narrow zone of beta-hemolysis on blood agar, with characteristic tumbling motility on wet mount.
Blood cultures & clinical course
Clinical course
Blood cultures drawn on admission grow the same organism as the CSF. Despite empiric treatment with ceftriaxone and vancomycin, she remains febrile with no improvement: standard empiric meningitis coverage does not reliably treat this pathogen.