Characterization of tmexCD-toprJ-positive Klebsiella spp. from pediatric patients in a Chinese hospital

The emergence of tmexCD-toprJ, a plasmid-mediated resistance-nodulation-division efflux pump gene cluster conferring resistance to tigecycline, poses a critical public health threat. While its prevalence among adults and within hospital settings has been extensively studied, its occurrence and epidemiological characteristics in pediatric populations remains scarcely reported and largely unknown. In this study, a total of 2,344 clinical Klebsiella isolates collected from pediatric patients (2019–2025) were screened for tmexCD-toprJ using PCR, and five positive isolates were identified. Antibiotic susceptibility via broth microdilution confirmed that all five isolates were multidrug-resistant, including one isolate resistant to almost all tested antimicrobial classes. Whole-genome sequencing and bioinformatics analysis were conducted to determine their genetic contexts. These strains were assigned to four distinct sequence types (STs): ST15, ST571, ST750-1LV, and ST3520-1LV, and exhibited diverse capsular locus types. Beyond tmexCD-toprJ, the five isolates also harbored carbapenemase genes (blaNDM−1, blaNDM−5, blaIMP−4, and blaOXA−1) and other antimicrobial resistance genes. The tmexCD-toprJ gene cluster was located on plasmids belonging to various incompatibility groups, including IncHI1B/IncFIB/IncR/IncN, IncHI1B/IncFIB, IncX3, and IncHI1B/IncFIB (Mar). However, conjugation assays demonstrated that these tmexCD-toprJ-carrying plasmids were non-transferable to the Escherichia coli recipients under the tested conditions. Taken together, this study reports the concerning co-harboring of tmexCD-toprJ with carbapenemase genes and other resistance determinants in Klebsiella spp. isolates recovered from pediatric patients in China. The presence of these resistance mechanisms on diverse genomic backgrounds highlights a significant clinical risk and underscores the urgent need for enhanced genomic surveillance and targeted strategies to preserve tigecycline efficacy in children.