Meropenem/vaborbactam activity against carbapenem-resistant Klebsiella pneumoniae from catheter-related bloodstream infections

Abstract

Introduction: Carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a significant threat in oncology settings due to its multidrug resistance and ability to form biofilms on indwelling medical devices.

Methods: This study investigated the in vitro and in vivo activity of meropenem/vaborbactam (MEV) against two CRKP isolates recovered from catheter-related bloodstream infections in patients undergoing orthopedic oncologic surgery.

Results: Whole-genome sequencing identified the isolates as ST101 and ST307, harboring resistance determinants including bla_KPC-3 and bla_OXA-1 , distributed across IncFII and IncFIB plasmid replicons. Both isolates exhibited extensive resistance to β-lactams, aminoglycosides, and fluoroquinolones but remained susceptible to MEV. Phenotypic assays revealed enhanced biofilm formation and metabolic activity compared to the reference strain Kp ATCC 13883 in the absence of hypervirulence-associated genes. MEV demonstrated bactericidal activity against both planktonic and biofilm-associated cells, with minimum bactericidal concentration (MBC₉₀) and minimum biofilm eradication concentration (MBEC₉₀) values of 0.5/8 μg/ml for CRKP ST101, 0.12/8 μg/ml for CRKP ST307, and 0.25/8 μg/ml for the Kp ATCC 13883 strain. In the Galleria mellonella infection model, MEV significantly improved larval survival following the CRKP challenge.

Discussion: These findings demonstrate that MEV exhibits activity against planktonic and biofilm-associated CRKP cells and highlight the need for further investigation in managing catheter-related bloodstream infections caused by multidrug-resistant K. pneumoniae.

Keywords: biofilm-associated infections; carbapenem-resistant Klebsiella pneumoniae; catheter-related bloodstream infections; meropenem/vaborbactam; multidrug-resistant plasmid; surgical site infection.

Figure 1

Antimicrobial susceptibility profiles and carbapenemase detection in Klebsiella pneumoniae strains. (A) Minimum inhibitory concentrations (MICs, μg/ml) for a panel of antibiotics were determined for CRKP ST101, CRKP ST307, and the reference strain K. pneumoniae ATCC 13883 using broth microdilution or automated systems, as appropriate. (B) Detection of carbapenemase enzymes was performed using a lateral flow immunoassay. Test bands indicate the presence of specific carbapenemases: IMP (I), VIM (V), NDM (N), KPC (K), and OXA-48-like enzymes (O). The control (C) band serves as an internal validity marker for test performance.

Figure 2

Phylogenetic analysis and genomic features of K. pneumoniae isolates. (A) A maximum-likelihood phylogenetic tree was constructed based on whole-genome sequences to assess the relatedness among K. pneumoniae strains. Isolates CRKP ST101 and CRKP ST307 (bold) are highlighted among reference genomes, revealing their phylogenetic placement. Genomes included in the analysis were filtered for high-quality completeness, and the presence of bla _KPC with metadata restricted to blood-derived isolates from European countries was confirmed. National flags indicate the country of origin. Sequence types (ST) and capsular loci (KL) are shown next to each genome. The presence or absence of bla _KPC or bla _OXA carbapenemase genes (red) are displayed in a binary heatmap. (B) Circular chromosomal maps of Klebsiella pneumoniae isolates CRKP ST101 and CRKP ST307. Chromosomal representations of CRKP ST101 (left) and CRKP ST307 (right) display annotated genomic features. Outer rings highlight predicted antimicrobial resistance (AMR) genes (red), biosynthetic gene clusters (blue), and relevant virulence or metabolic determinants. Inner rings display GC content (black), GC skew+ (green), and GC skew– (purple). Biosynthetic clusters include RIPP-like, nonribosomal peptide synthetase (NRP)-metallophore, azole-containing RIPP, and terpene precursor regions.

Figure 3

Phylogenetic tree of plasmids carrying carbapenemase genes bla _KPC and/or bla _OXA in K. pneumoniae. Plasmid sequences were clustered based on sequence similarity and colored according to the presence of bla _KPC (yellow), bla _OXA (purple), or both genes (orange). Plasmids (p) from CRKP ST101 and CRKP ST307 are highlighted (bold). The matrix on the right displays the presence (green) or absence (white) of plasmid replicons across plasmid genomes.

Figure 4

Virulence-associated traits in K. pneumoniae clinical isolates. (A) Quantitative analysis of biofilm biomass, (B) metabolic activity of planktonic cells, (C) capsule production, (D) and siderophore secretion in CRKP ST101, CRKP ST307, and Kp ATCC 13883. Statistical significance was determined using a one-way ANOVA followed by Tukey’s multiple comparisons test (p < 0.05). (E) A representative image of the string test performed on Kp ATCC 13883 to assess the hypermucoviscous phenotype. *P < 0.05; **P < 0.01; ***P < 0.001, ****P < 0.0001.

Figure 5

Antibacterial activity of MEV against K. pneumoniae planktonic and biofilm-associated cells. Bacterial survival was quantified following treatment with increasing concentrations of MEV and expressed as the percentage of CFU/ml relative to untreated controls. Data are shown for CRKP ST101, CRKP ST307, and the reference strain K. pneumoniae ATCC 13883 under planktonic and biofilm-associated conditions. The color gradient indicates growth compared to the untreated controls. The dashed black horizontal line indicates the 90% reduction threshold used to define the minimum bactericidal concentration (MBC₉₀) for planktonic cells and the minimum biofilm eradication concentration (MBEC₉₀) for biofilm-associated cells.

Figure 6

Kaplan-Meier survival curves of G. mellonella infected with K. pneumoniae and treated with MEV. (A) Schematic representation of the G. mellonella infection model, illustrating the injection procedure and representative images of healthy (light-colored) and dead (dark-colored) larvae. (B) Survival of G. mellonella following infection with Kp ATCC 13883 at inocula of 1×10³, 1×10⁴, and 1×10⁵ CFU/larva over 48 hours. (C) Comparative survival analysis of G. mellonella infected with Kp ATCC 13883, CRKP ST101, and CRKP ST307 at 1×10⁵ CFU/larva. (D–F) Kaplan-Meier survival curves of G. mellonella infected with Kp ATCC 13883 (D), CRKP ST101 (E), or CRKP ST307 (F) at 1×10⁵ CFU/larva and treated with a single dose of MEV (2g meropenem + 2g vaborbactam equivalent) administered 30 minutes post-infection. Control groups included larvae treated with either MEV (2 g/2 g equivalent) or PBS (Data not shown). Statistical significance was determined using the Log-rank test. *P < 0.05; **P < 0.01.