Investigation of virulence and carbapenem resistance genes, antibiotic resistance pattern, epidemiological characteristics and risk factors of hypermucoviscous Klebsiella pneumoniae clinical isolates

Objective: The objective of this study is to investigate the virulence and carbapenem resistance genes, antibiotic resistance patterns, epidemiological characteristics, and risk factors of hypermucoviscous K. pneumoniae (HmKp) clinical isolates obtained from various clinical specimens. Material and Methods: In this study, 136 K. pneumoniae strains isolated at the Medical Microbiology Laboratory of Karadeniz Technical University Faculty of Medicine between April 2023 and April 2025 were examined. Hypermucoviscosity of the isolates was assessed using the string test, antibiotic susceptibilities were determined by disk diffusion test and BD Phoenix M50™ (Becton Dickinson Diagnostic Instrument Systems, Sparks, Md, ABD) automated system, virulence and carbapenemase genes were investigated by polymerase chain reaction (PCR), and molecular epidemiology was analyzed using the multilocus sequence typing (MLST) method. Among the HmKp strains, iucA gene positive strains were accepted as hypervirulent Klebsiella pneumoniae (HvKp). Results: In our study, 68 hypermucoviscous and 68 non-hypermucoviscous strains were identified. Of the 68 hypermucoviscous strains, 16 were identified as having the iucA gene and were accepted as HvKp. Although the hypermucoviscous strains were generally more susceptible to antibiotics, a higher resistance rate was observed for cefiderocol. The most common carbapenemase type identified was KPC. 12 of the strains were blaKPC, 9 were blaOXA-48 and 1 was blaNDM positive. Of the HvKp strains, 6 (37.5%) were carbapenem resistant HvKp (KD-HvKp). Among the KD-HvKp strains, 3 were blaKPC, 2 were blaOXA-48 and 1 was blaNDM positive. The virulence genes rmpA, rmpA2, iucA, iroB as well as the K2 gene, were found to be associated with hypermucoviscosity. Sequence typing was performed for 11 HmKp strains. High-risk types such as ST307 and ST2096 were identified. Certain risk factors such as diabetes, invasive disease were found to be associated with hypermucoviscosity and hypervirulence. Conclusion: Our study has demonstrated the presence of HvKp isolates in our region that are associated with high-risk clones worldwide and harbor carbapenemase genes. Especially, the detection of HvKp strains that carry carbapenemase genes and are resistant to cefiderocol is alarming. These findings are of great importance for defining the epidemiological characteristics and treatment of HvKp, and provide fundamental data for developing prevention and control strategies. The association of certain risk factors with HmKp and HvKp infections suggests that these factors may be useful in predicting such infections.