Multifocal Early-Onset Neonatal Listeriosis with Discordant GradientStrip Ampicillin Non-Susceptibility: A Case Report

Background: Early-onset neonatal listeriosis is a rare, life-threatening infection of vertical origin caused by Listeria monocytogenes. First-line therapy is intravenous ampicillin combined with an aminoglycoside; acquired β-lactam resistance is exceptionally uncommon. Case Presentation: A 34-week preterm female neonate (birth weight 1990 g, appropriate for gestational age) was born to a febrile primigravida with fetid greenish amniotic fluid at a regional secondary maternity and transferred at 30 h of life to our tertiary NICU with respiratory failure requiring mechanical ventilation. L. monocytogenes was recovered from blood, gastric aspirate, pharyngeal exudate, ocular secretion, and skin swab. Gradient strip susceptibility testing reported ampicillin and trimethoprim–sulfamethoxazole non-susceptibility, although confirmatory broth microdilution was unavailable. Broad-spectrum empirical therapy was revised on Day 5 to include ampicillin–sulbactam, with piperacillin–tazobactam and gentamicin continued. A follow-up blood culture on Day 9 remained sterile through 7 days. The hospital course was complicated by thrombocytopenia, transiently elevated aminotransferases, and a Grade I subependymal hemorrhage; tertiary NICU length of stay was 25 days. Conclusions: Recovery under a multi-agent regimen precludes attribution of effect to any single component. Discordant gradient strip susceptibility results in L. monocytogenes should be confirmed by broth microdilution before any therapeutic change; survivors of severe early-onset listeriosis require structured multidisciplinary follow-up.