Resistance, Virulence, and Molecular Epidemiology of Carbapenem-Resistant Klebsiella pneumoniae Causing Bloodstream Infections in Saudi Arabia

Carbapenem-resistant <i>Klebsiella pneumoniae</i> (CRKP) has become a major cause of bloodstream infections and poses serious challenges to clinical management because treatment options are limited. This study aimed to characterize antimicrobial resistance, virulence-associated features, and molecular epidemiology of CRKP bloodstream isolates using integrated phenotypic and genomic approaches. A total of 74 non-duplicate CRKP isolates were collected from bloodstream infections at three tertiary-care hospitals in Riyadh, Saudi Arabia, between 2022 and 2024. All isolates showed classical <i>Klebsiella pneumoniae</i> phenotypic characteristics, including intrinsic resistance to natural and aminopenicillins, and were classified as either multidrug-resistant (MDR) or extensively drug-resistant (XDR). Resistance to imipenem was universal, and resistance to other β-lactams and fluoroquinolones was high. Carbapenemase genes were detected in 96.0% of isolates using the GeneXpert^® Carba-R assay, with <i>bla</i>_OXA-48-like and <i>bla</i>_NDM being most common. Whole-genome sequencing demonstrated predominance of Ambler class D carbapenemases, particularly <i>bla</i>_OXA-232, with additional contributions from <i>bla</i>_NDM-1 and <i>bla</i>_NDM-5. Co-occurrence of carbapenemase genes was observed in a subset of isolates. Virulence analysis showed that 37.8% of isolates exhibited a hypermucoviscous phenotype, and more than half carried at least one virulence-associated determinant linked to capsule regulation or iron acquisition. In contrast, most isolates showed weak or no biofilm-forming capacity. Multilocus sequence typing revealed substantial genetic diversity but clear dominance of high-risk lineages, particularly ST147 and the emerging ST2096, both closely associated with <i>bla</i>_OXA-232 and <i>bla</i>_OXA-48-like genes. Capsular and O-antigen analysis showed a non-random distribution dominated by KL64 and O1/O2. Phylogenetic analysis was consistent with clonal expansion and suggested intra-hospital spread, with the intensive care unit serving as a key reservoir and dissemination to other wards. In conclusion, CRKP bloodstream infections in this setting are largely associated with a limited number of epidemic clones that combine extensive antimicrobial resistance with virulence-associated traits. These findings support the need for ongoing genome-based surveillance, strengthened infection control measures, and antimicrobial stewardship to limit the spread of high-risk <i>K. pneumoniae</i> lineages in healthcare settings.