Listeria monocytogenes meningoencephalitis in an immunocompetent patient: Report of an unusual case and review of the literature

Introduction: Listeria monocytogenes is an intracellular Gram-positive bacterium responsible for serious infections, especially meningoencephalitis, in immunocompromised individuals, pregnant women, and neonates. However, cases in immunocompetent individuals are rare and underdiagnosed. 
Case presentation: A previously healthy 34-year-old woman presented with severe headache, fever, and altered mental status. Cerebrospinal fluid (CSF) analysis revealed mononuclear pleocytosis, hypoglycorrhachia, and elevated protein levels. Culture and PCR identified Listeria monocytogenes. She was treated with ampicillin and gentamicin for 21 days, with complete recovery. 
Discussion: This case demonstrates Listeria 's ability to cause meningoencephalitis even in patients without predisposing factors. Dietary factors, bacterial virulence, and individual genetic susceptibility may contribute to the clinical presentation. Relevant pathophysiological, diagnostic, and therapeutic aspects are reviewed. 
Conclusion: Listeria monocytogenes should be considered in the differential diagnosis of subacute bacterial meningitis in young adults, especially in contexts of high-risk food exposure.