Epidemiological and Genomic Insights into Linezolid-Non-Susceptible Enterococci in Pediatric Patients.

Enterococci are major opportunistic pathogens causing healthcare-associated infections in children. Linezolid, a WHO-designated critically important antibiotic for multidrug-resistant Gram-positive infections, is increasingly challenged by linezolid-non-susceptible enterococci (LNSE). Yet pediatric LNSE epidemiology and genomics data remain scarce, hindering targeted control. We analyzed 26 LNSE strains isolated from Children's Hospital, Zhejiang University School of Medicine (June 2020-July 2024) using MALDI-TOF MS, Vitek2 Compact, micro-broth dilution (for linezolid MIC), MLST, resistance/virulence gene detection, and pan-genome analysis (COG/KEGG annotation). Enterococcus faecalis (E. faecalis) dominated (23/26,88.5%) with ST16 as the major sequence type (ST) and four novel STs identified; all strains harbored optrA and fexA, with species-specific resistance/virulence gene profiles. The 23 E. faecalis strains exhibited an open pan-genome (b = 0.174725), indicating the possible existence of active horizontal gene transfer (HGT), with core, accessory, and unique genes showing distinct functional differentiation. These findings provide critical and robust empirical data to inform the development of targeted prevention and control strategies against LNSE in pediatric populations.