# Characterization of Klebsiella pneumoniae Isolates Resistant to Cefiderocol from Hospitals and Outpatient Settings in Croatia

## TL;DR

This study characterizes cefiderocol-resistant Klebsiella pneumoniae isolates in Croatia, revealing their antibiotic resistance profiles and genetic traits.

## Contribution

This is the first study in Croatia on cefiderocol resistance in Klebsiella pneumoniae, highlighting its spread in both hospital and outpatient settings.

## Key findings

- All 31 isolates showed high resistance to multiple antibiotics, including amoxicillin–clavulanate and cefepime.
- 61% of isolates carried the blaOXA-48 gene, while 29% and 12.9% carried blaKPC and blaNDM genes, respectively.
- Ceftazidime–avibactam and colistin showed preserved activity against 87% and 71% of isolates, respectively.

## Abstract

Background/Objectives: We conducted this study to evaluate the genotypic and phenotypic profiles of carbapenem-resistant Klebsiella pneumoniae (CRKP) isolates, exhibiting resistance to cefiderocol (FDC), focusing on antibiotic susceptibility, β-lactamase production, the genetic environment of blaCARB and blaESBL genes and molecular epidemiology. FDC is now a last-line antibiotic for severe infections due to CRKP. Methods: Susceptibility to a wide range of antibiotics was determined by the disk diffusion and broth microdilution method. Carbapenemases were screened by a modified Hodge test while carbapenem hydrolysis was investigated using mCIM and eCIM tests. The screening for β-lactamase and fluoroquinolone cluster resistance genes was carried out by PCR. Plasmids were characterized by PCR-based replicon typing (PBRT). An inter-array genotyping CarbaResist test and whole genome sequencing (WGS) were applied on selected isolates. Results: All of the 31 isolates studied exhibited high-level resistance to amoxicillin–clavulanate, piperacillin–tazobactam, cefuroxime, expanded-spectrum cephalosporins (ESC), cefepime, ceftolozan–tazobactam and ciprofloxacin and the majority to gentamicin, and amikacin. Colistin and ceftazidime–avibactam preserved activity against 71% and 87% of the isolates, respectively. The combined disk method with clavulanic acid was positive in all but one isolate, indicating the production of an ESBL. Twenty-eight isolates carried one single carbapenemase-encoding gene, whereas three harbored double blaCARB genes. Among the studied isolates, 61% carried blaOXA-48, 29% blaKPC and 12.9% blaNDM genes. The inter-array genotyping CarbaResist test and WGS identified additional aminoglycoside-, sulphonamide- and trimethoprim-resistance genes. Conclusion: To our knowledge, this is the first study on FDC resistance in Croatia. The diffusion of FDC-resistant isolates was detected in both hospital and outpatient settings, emphasizing the need for a “One Health” approach.