Discordance between in vitro susceptibility and clinical response in early-onset neonatal sepsis caused by Morganella morganii: a case report in an extremely preterm infant.

Early-onset neonatal sepsis (EONS) caused by Morganella morganii is rare, particularly in extremely preterm infants, and poses diagnostic and therapeutic challenges. We report a case of EONS in an extremely preterm neonate in whom blood cultures identified Morganella morganii with in vitro susceptibility to gentamicin, which was initiated as part of the empirical treatment. Despite documented antimicrobial sensitivity, the infant showed no significant clinical improvement. Consequently, antibiotic therapy was modified based on both susceptibility testing and the evolving clinical picture, resulting in marked clinical recovery. This case highlights that antimicrobial susceptibility results should be interpreted in conjunction with the patient's clinical response and that treatment decisions in neonatal sepsis should not rely solely on in vitro sensitivity patterns, particularly when dealing with uncommon pathogens.