Epidemiological and functional insights into iroBCDN loss in ST11 carbapenem-resistant hypervirulent Klebsiella pneumoniae

ABSTRACT Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) has emerged as a major public health threat due to its high virulence, multidrug resistance, and increasing global prevalence. However, the molecular characteristics and adaptive mechanisms underlying the CR-hvKP pathogenesis remain poorly understood. In this study, we collected 217 CRKP isolates from a tertiary hospital and identified 46 as CR-hvKP. Genomic analysis revealed that the majority of CR-hvKP strains belonged to ST11-KL64 (48.7%, 20/46) and ST11-KL25 (46.3%, 19/46), followed by ST11-KL47 (4.8%, 2/46). Interestingly, while iroBCDN was present in various sequence types, it was found in ST11 strains only with the KL47 capsule type, which showed high virulence in Galleria mellonella models. To investigate the biological role of iroBCDN , we constructed an iroBCDN deletion mutant and a complemented strain in an ST11-KL47 background. The lactate dehydrogenase cytotoxicity assays and G. mellonella infection models revealed no significant difference in virulence among the wild-type, knockout, and complemented strains. Remarkably, phenotypic assays showed that the iroBCDN deletion mutant exhibited enhanced growth fitness, competitive advantage, oxidative stress resistance, and survival in human whole blood. Transcriptomic analysis revealed that iroBCDN deletion led to the upregulation of genes involved in oxidative stress response, capsule biosynthesis, and energy metabolism, while genes related to fimbrial assembly and carbon metabolism were downregulated. These findings suggest that the loss of iroBCDN does not attenuate virulence in ST11 CR-hvKP but instead enhances its environmental adaptability, potentially contributing to the persistence and dissemination of epidemic clones. IMPORTANCE The emergence of carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) poses a severe global health threat. This study reveals a critical paradox: deletion of the iroBCDN locus traditionally associated with virulence does not attenuate pathogenicity in ST11-KL47 CR-hvKP. Instead, its loss significantly enhances bacterial fitness by improving growth competitiveness, oxidative stress resistance, and survival in human blood. It demonstrates how loss of specific genetic elements may facilitate the dominance of high-risk clones like ST11-KL64/KL25 by optimizing environmental adaptation and persistence—key factors in hospital transmission. Understanding this fitness trade-off is vital for developing strategies against resilient CR-hvKP epidemics.