Gram-negative bacillary meningitis

Introduction
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By Ravindra Kumar Garg MD

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 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. 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. Acinetobacter meningitis is becoming an increasingly common cause of meningitis in post-neurosurgical patients. One report suggests that gram-negative micro-organisms were the most frequent causal agents identified in patients with external ventricular drain-related infections (meningitis or ventriculitis). The exact pathogenesis of gram-negative meningitis is not completely understood. A meta-analysis suggests that prophylactic antibiotics administered before craniotomy reduce rates of postoperative meningitis by one half. Some older antibiotics like polymyxins have been found useful for the treatment of several intensive care unit-acquired infections including meningitis. Combination antibiotic treatment with intraventricular gentamicin was found an effective and safe alternative. In this updated summary, Dr R K Garg reviewed 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.
  • 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.