# In Vitro Activity of Cefiderocol Against Multi-Drug-Resistant Gram-Negative Clinical Isolates in Romania

## TL;DR

This study tests how well cefiderocol works against drug-resistant Gram-negative bacteria in Romania, finding mixed effectiveness and highlighting the risk of resistance spreading.

## Contribution

The study provides new insights into cefiderocol's efficacy against MDR Gram-negative isolates in a Romanian clinical setting.

## Key findings

- Cefiderocol showed 52.8% susceptibility against MDR Gram-negative isolates, with higher rates in Enterobacterales.
- All P. aeruginosa isolates were susceptible to cefiderocol, but A. baumannii showed lower and variable susceptibility.
- NDM-only isolates were resistant to cefiderocol, while some NDM and OXA-48 co-harboring isolates remained susceptible.

## Abstract

Background/Objectives: Gram-negative bacteria with acquired carbapenem resistance have become increasingly common in serious infections. This study aimed to evaluate the in vitro activity of cefiderocol against multidrug-resistant Gram-negative clinical isolates collected from a tertiary care hospital in Romania. Methods: A retrospective study (November 2024–February 2025) involving 89 consecutive Multi-Drug Resistant (MDR) Gram-negative isolates, 66 Enterobacterales and 23 non-fermenters (P. aeruginosa, S. maltophilia, A. baumannii), was conducted. Results: Overall, 52.8% of Enterobacterales and P. aeruginosa isolates were susceptible to cefiderocol, with higher susceptibility among Enterobacterales alone (63.6%). Using disk diffusion, 66.3% of all isolates were classified as susceptible to the antibiotic. K. pneumoniae isolates co-harboring NDM and OXA-48 were susceptible in 65.3% of cases, while NDM-only producers were resistant. All P. aeruginosa isolates tested were susceptible to the antibiotic. Susceptibility rates in A. baumannii were lower (68.8%), with variability between testing methods. Conclusions: The presence of NDM-producing isolates with complete resistance to cefiderocol in our study highlights the risk that resistance may spread rapidly once the drug becomes widely used. Cefiderocol may be an effective option for treating MDR bacterial infections, but strict microbiological monitoring remains essential.