Phylogenetic structure and clinical implications of carbapenemase-aerobactin (iuc) convergence in respiratory Klebsiella pneumoniae from a tertiary hospital in China, 2017–2023

Objectives To characterise the phylogenetic structure and clinical implications of carbapenemase–aerobactin ( iuc ) convergence among respiratory Klebsiella pneumoniae isolates. Methods We performed whole-genome sequencing of 707 non-duplicate respiratory K. pneumoniae isolates collected at a tertiary hospital in China from 2017 to 2023 and linked the genomic data to blinded clinical adjudication. Isolates were grouped by carbapenemase gene carriage and iuc status. Core-genome SNP phylogenies were constructed for ST11 and ST23, and reference-plasmid mapping to pK2044 was performed in a targeted subset. Within the carbapenemase-positive subset, logistic regression was used to test the incremental contribution of iuc beyond age, Charlson Comorbidity Index, and ICU admission during hospitalisation. All-cause mortality at 14, 28, and 90 days was assessed among infection cases. Results Overall, 548/707 isolates (77.5%) were adjudicated as infection, including 280 community-acquired pneumonia and 268 hospital-acquired pneumonia cases. Seventy-nine isolates (11.2%) were classified as carb + / iuc + , and 74/79 (93.7%) belonged to ST11. Phylogenetic analysis showed that convergence was concentrated in lineage-restricted ST11 branches, particularly KL64/KL47-associated backgrounds, whereas ST23 formed a more dispersed classical iuc -positive lineage background. Carb − / iuc + ST23 retained a conserved hypervirulence-associated module and showed high compatibility with pK2044, whereas carb + / iuc + ST11 showed a more fragmented virulence profile and heterogeneous, incomplete pK2044 coverage. Within the carbapenemase-positive subset, adding iuc to a model including age, Charlson Comorbidity Index, and ICU admission during hospitalisation did not improve infection attribution (adjusted OR 0.93, 95% CI 0.33–2.68; likelihood ratio test P = 0.892; ΔAIC = 1.98). Among infection cases, carb + / iuc + and carb + / iuc − groups showed broadly similar all-cause mortality at 14, 28, and 90 days. Conclusions Carbapenemase–aerobactin convergence among respiratory K. pneumoniae was concentrated in dominant ST11 backgrounds and occurred in distinct lineage-specific virulence contexts. However, within the carbapenemase-positive respiratory subset, iuc added limited value for infection attribution and did not clearly separate short- to intermediate-term mortality beyond host and care-setting factors.