Silent carriage of tigecycline- and carbapenem-resistant Klebsiella quasipneumoniae co-harbouring tetX(4) and blaNDM-1 in healthy individuals in China.

Abstract

OBJECTIVES: To investigate the occurrence and genomic characteristics of tigecycline- and carbapenem-resistant Klebsiella quasipneumoniae isolated from healthy individuals in China. METHODS: During a nationwide screening programme, faecal samples from healthy community individuals were cultured for carbapenem-resistant Enterobacterales. Antimicrobial susceptibility testing, whole-genome sequencing and conjugation assays were performed for two K. quasipneumoniae isolates co-harbouring tet(X4) and blaNDM-1. RESULTS: Two K. quasipneumoniae strains carrying tet(X4) and blaNDM-1 were recovered from healthy individuals without recent hospitalisation or antibiotic exposure. Both isolates showed resistance to tigecycline (>8 μg/mL) and carbapenems (≥4 μg/mL). Genomic analysis demonstrated close clonal relatedness between the isolates (ST6460-1LV, KL151). The blaNDM-1 gene was located on an IncX3 plasmid associated with mobile genetic elements, whereas tet(X4) was carried by an IncX1 plasmid. Conjugation assays confirmed successful transfer of both resistance genes, which frequently co-transferred into recipient strains. CONCLUSIONS: To our knowledge, this is the first report of K. quasipneumoniae co-harbouring tet(X4) and blaNDM-1 in healthy individuals in China. The findings indicate that healthy community populations may serve as a hidden reservoir for last-resort antimicrobial resistance genes and underscore the importance of community-based surveillance within a One Health framework.