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  • Updated 07.07.2023
  • Released 03.06.1997
  • Expires For CME 07.07.2026

Gram-negative bacillary meningitis



Gram-negative bacilli are common organisms in nosocomial meningitis in adults. Escherichia coli containing the K1 capsule is the leading cause of Gram-negative meningitis in neonates. In patients with Gram-negative bacterial meningitis, Acinetobacter baumannii is emerging as an important causative agent. Nosocomial Gram-negative bacterial meningitis is a complication of a variety of surgical procedures, such as craniotomy, placement of internal or external ventricular catheters, lumbar puncture, intrathecal infusions, or spinal anesthesia; head injury; or at times secondary to metastatic infection in patients with hospital-acquired bacteremia. An outbreak of meningitis and spinal infections with Gram-negative bacteria following local injections for the treatment of chronic back pain was reported in Germany. Gram-negative meningitis may occur following endoscopic endonasal transsphenoidal surgery, but the frequency is quite low. HIV infection predisposes spontaneous Gram-negative bacillary meningitis. Escherichia coli, Klebsiella, and Pseudomonas species cause 20% to 28% of early-onset infant bacteremia and 14% cases of infant meningitis globally, particularly in low- and middle-income countries. The mortality and morbidity associated with Gram-negative meningitis have remained significant despite advances in antimicrobial chemotherapy. Some patients lack many of the classic features of bacillary meningitis, especially the elderly, and pose a diagnostic challenge. CSF culture is the most important test to establish the diagnosis of Gram-negative meningitis. Metagenomic next-generation sequencing is now a widely used molecular technology that rapidly detects Gram-negative bacteria in CSF specimens of patients with nosocomial meningitis. The exact pathogenesis of Gram-negative meningitis is not completely understood. A meta-analysis showed that combined intraventricular antibiotic plus intravenous treatment was not superior to standard intravenous-only treatment in nosocomial ventriculitis/meningitis. In this article, the author reviews the latest information on the clinical features, etiology, pathogenesis, treatment, and outcome of Gram-negative bacillary meningitis.

Key points

• Gram-negative bacilli are major causative agents of meningitis in the neonatal period.

Escherichia coli carrying the K1 capsular antigen is the most common Gram-negative bacillary organism causing neonatal meningitis.

• Nosocomial Gram-negative bacterial meningitis may occur as a complication of neurosurgical procedures, head injury, or secondary to metastatic systemic infection.

• Gram-negative bacilli can be rare causes of spontaneous meningitis in adults, including individuals without risk factors.

• Third-generation cephalosporins are highly active against most Gram-negative bacilli and have excellent CSF penetration.

• Although effective against Gram-negative infections outside the central nervous system, systemically administered aminoglycosides, such as gentamicin, have very poor penetration across the meninges, even in the presence of meningitis.

• Mortality and long-term sequelae rates are high among adults and children with Gram-negative bacterial meningitis.

Historical note and terminology

"Gram-negative meningitis" is a term generally used to encompass those infections of the CSF and meninges due to bacteria such as Enterobacteriaceae and Pseudomonas aeruginosa occurring beyond the neonatal period, exclusive of Neisseria meningitis and Haemophilus influenzae, although some authors use the term to include all of the above. Occasional reports of Gram-negative bacillary meningitis date from as early as the 19th century. Case descriptions of Gram-negative meningitis following abortions, genitourinary procedures, and spinal anesthesia began to appear with some frequency in the 1930s and 1940s. An early literature review of 100 cases of Gram-negative meningitis found that most infections occurred in the neonatal period (05). The first large series of adults with Gram-negative meningitis was described in soldiers who suffered head injuries during World War II (41). Subsequent reports largely characterized Gram-negative meningitis as a nosocomial infection in adults who had undergone neurosurgical procedures (23; 45).

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