Deletion of peg-344 Attenuates Systemic Virulence and Is Associated with Repression of the Histidine Utilization System in a Carbapenem-Resistant Hypervirulent Klebsiella pneumoniae Clinical Isolate

PEG-344 is a predicted metabolite transporter implicated in the virulence of hypervirulent Klebsiella pneumoniae, but its role in carbapenem-resistant hypervirulent K. pneumoniae (CR-hvKp) remains unclear. We investigated KPL1, an ST11-KL62 CR-hvKp isolate carrying a peg-344-positive virulence plasmid. An isogenic peg-344 deletion mutant was evaluated using growth assays, an intraperitoneal infection model in male C57BL/6J mice, RNA sequencing, quantitative real-time PCR, and untargeted and targeted metabolomics. Deletion of peg-344 did not cause sustained growth impairment, but prevented mortality over 168 h, reduced organ bacterial burdens by 2–3 log10 CFU/g, and reduced biochemical evidence of hepatic and renal injury. RNA sequencing identified 88 differentially expressed genes, including coordinated downregulation of six histidine utilization (HUT) system genes. Histidine metabolism was significantly enriched, and selected changes were confirmed by qRT-PCR. Histidine-related metabolites were not significant after false-discovery-rate correction in untargeted metabolomics. Targeted UHPLC–MS/MS analysis showed numerically lower mean L-histidine concentrations in mutant-derived samples, although the differences were not statistically significant. These findings extend evidence for peg-344 deletion-associated virulence attenuation to an ST11-KL62 CR-hvKp background and identify coordinated HUT-system repression as a prominent transcriptional response. Because complementation and direct transport assays were not performed and the omics samples were non-matched, these associations do not establish a direct substrate or causal mechanism.