Corynebacterium amycolatum: an underestimated pathogen in early-onset neonatal sepsis-a case report

Early-onset neonatal sepsis (EOS) is a critical condition primarily caused by maternal-fetal transmission of bacterial pathogens during delivery, with Escherichia coli and Group B Streptococcus being the most prevalent. However, neonatal sepsis can also involve other rare bacteria, including Corynebacterium amycolatum, which was first described in 1988 and is widely recognized as an emerging pathogen in infectious diseases.

A male infant was admitted to the neonatal intensive care unit (NICU) due to premature birth and tachypnea. His mother had experienced premature rupture of membranes (PROM) 20 days prior. The infant's procalcitonin (PCT) level was significantly elevated, reaching 1.51 ng/ml. Chest X-ray revealed increased and blurred lung markings, slightly decreased lung transparency in both lung fields, with scattered ground-glass opacities, and a few fine granular shadows. Corynebacterium amycolatum was isolated from the blood cultures and identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) with 99.9% confidence. Antimicrobial susceptibility testing showed that the isolate was sensitive to penicillin, cephalosporins, and vancomycin, yet resistant to ciprofloxacin, clindamycin, and erythromycin. Empirical treatment with ampicillin and cefoperazone/sulbactam was initially started. Followed by ceftazidime based on susceptibility results, the infant's condition significantly improved, leading to discharge.

This case emphasizes the importance of recognizing C. amycolatum as a potential pathogen in neonatal sepsis, especially in preterm infants, and underscores the necessity of accurate identification methods such as MALDI-TOF MS to avoid misidentification. Given the severe clinical outcomes associated with this condition, heightened awareness and diagnostic precision are crucial for optimizing treatment strategies in neonatal intensive care units. This report highlights a rare case of EOS caused by C. amycolatum in a premature infant.