Gram-negative bacillary meningitis

Ravindra Kumar Garg MD (Dr. Garg of King George's Medical University in Lucknow, India, has no relevant financial relationships to disclose.)
John E Greenlee MD, editor. (

Dr. Greenlee of the University of Utah School of Medicine has no relevant financial relationships to disclose.

Originally released March 6, 1997; last updated April 19, 2019; expires April 19, 2022

This article includes discussion of Gram-negative bacillary meningitis, Gram-negative bacterial meningitis, Gram-negative meningitis, nosocomial meningitis, and postneurosurgical 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. 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. Gram-negative meningitis does occur following endoscopic endonasal transsphenoidal surgery, but frequency is quite low. HIV infection predisposes spontaneous Gram-negative bacillary meningitis. 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. The exact pathogenesis of Gram-negative meningitis is not completely understood. A metaanalysis 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 common causative agents of meningitis in the neonatal period.


• Gram-negative bacilli rarely cause meningitis in adults without risk factors.


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


• Nosocomial bacterial meningitis is a complication variety of neurosurgical procedures, head injury, or secondary to metastatic infection.


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


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


• 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, though case descriptions 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 (Barrett et al 1942). The first large series of adults with Gram-negative meningitis was described in soldiers who suffered head injuries during World War II (Lewin 1948). Subsequent reports largely characterized Gram-negative meningitis as a nosocomial infection in adults who had undergone neurosurgical procedures (Gorman et al 1962; Mangi et al 1975).

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