Carbapenem-resistant Klebsiella pneumoniae has emerged as a major cause of healthcare-associated infections, driven by the global dissemination of high-risk clones. Because chlorhexidine is widely use...

Although the incidence of ESBL-infected <i>K. pneumoniae</i> in veterinary settings is worrisome, PKp-V1 phages showed considerable lytic action against the host bacterium, indicating the potential of PKp-V1 as a possible alternative therapeutic option against MDR <i>K. pneumoniae</i>.

KP ST258 is an epidemic lineage of multidrug-resistant gram-negative bacteria that has caused numerous outbreaks in hospitals around the world. The KP ST258 population is divided into two genetically related but distinct clades, which differ primarily in their capsule type. In this study, we found that patients infected with one of the KP ST258 clades were more acutely ill than patients infected with the other clade. We also observed clade-specific differences both in killing by human serum and in bacterial dissemination in a mouse model of pneumonia. Finally, we identified important limitations in the use of mouse models to study host defenses against multidrug-resistant KP infection. Overall, this work underscores the importance of capsule composition in KP ST258 virulence, identifies differences in the host response to KP infection between mice and humans, and highlights a potential role for complement-targeting immunotherapeutics in the treatment of KP infections.

The epidemiology of carbapenem-resistant Klebsiella pneumoniae (CRKP) must be monitored over time to understand resistance dynamics to existing and novel antibiotics.MethodsAntibiotic susceptibility testing and whole-genome sequencing were performed on clinical CRKP isolates collected from the same California long-term acute care hospital network across two time periods: 2014-15 (period 1) and 2021-23 (period 2). Differences in sequence type (ST) diversity, carbapenem resistance-associated genotypes, and resistance to clinically important antibiotics were evaluated.ResultsEight hundred eighty-one isolates were collected (period 1, 374; period 2, 507). Study period 1’s population was dominated by ST258 (94.1%). ST diversity markedly increased in period 2, with a reduced prevalence of ST258 (41.6%) and an increased abundance of other epidemic lineages: ST14 (27.4%), ST307 (6.9%), and ST17 (6.5%). Changes to circulating resistance genotypes and plasmids reflected the increased ST diversity. Increases in blaKPC-3-harboring isolates (66.0% vs. 76.1%) and non-carbapenemase-containing isolates (2.7% vs 12.6%) aligned with decreases in blaKPC-2-harboring isolates (30.5% vs. 6.3%). Statistically significant differences in resistance patterns were also observed between study periods, including colistin (35.0% vs. 20.2%), fosfomycin (27.0% vs. 13.4%), meropenem-vaborbactam (9.4% vs. 2.0%), and ceftazidime-avibactam (1.1% vs. 9.1%). Differential patterns of resistance emergence and spread across circulating STs largely drove resistance patterns in study period 2.ConclusionsThe comparison of clinical CRKP isolates collected from the same healthcare network and separated by nearly a decade revealed increasing ST diversity, mainly due to the introduction of numerous epidemic lineages, which coincided with differing patterns of circulating resistance-associated genotypes and antibiotic resistance.

ABSTRACTCefiderocol (CFDC) is a siderophore-conjugated cephalosporin developed to overcome multidrug resistance in gram-negative bacteria. Despite its unique iron-dependent entry mechanism, CFDC resistance has emerged in Klebsiella pneumoniae, primarily driven by alterations in siderophore transport and β-lactamase evolution; however, the broader intrinsic resistome that supports CFDC tolerance remains incompletely defined. Here, we performed high-density transposon mutagenesis (Tn-Seq) in the epidemic ST258 K. pneumoniae to map the functional genetic landscape of CFDC susceptibility. Tn-Seq identified siderophore uptake components (tonB and cirA) as the dominant determinants of CFDC resistance. In contrast, disruption of genes involved in peptidoglycan recycling (ampG and ldcA), synthesis (mrcB and lpoB), and enterobacterial common antigen biosynthesis (wzxE and wzyE), as well as deletion of plasmid-encoded blaKPC-3, increased CFDC susceptibility. In a CFDC-resistant ΔtonB strain, targeting these envelope homeostasis pathways yielded only limited resensitization relative to the siderophore-competent parental strain. Deletion of blaKPC-3 produced the greatest increase in susceptibility, reducing the CFDC MIC fourfold. This pattern is consistent with a model in which reduced CFDC influx in the ΔtonB background lowers intracellular drug exposure to levels at which the otherwise limited anti-CFDC activity of KPC β-lactamase becomes sufficient to drive resistance. Together, these data support a multi-layered functional network governing cefiderocol susceptibility in ST258 K. pneumoniae, in which iron-dependent drug uptake constrains intracellular exposure, while β-lactamase activity and intrinsic envelope homeostasis pathways further shape bacterial tolerance once cefiderocol enters the cell.