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

<b>Background/Objectives</b>: 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. <b>Methods</b>: A retrospective study (November 2024-February 2025) involving 89 consecutive Multi-Drug Resistant (MDR) Gram-negative isolates, 66 <i>Enterobacterales</i> and 23 non-fermenters (<i>P. aeruginosa</i>, <i>S. maltophilia</i>, <i>A. baumannii</i>), was conducted. <b>Results</b>: Overall, 52.8% of <i>Enterobacterales</i> and <i>P. aeruginosa</i> isolates were susceptible to cefiderocol, with higher susceptibility among <i>Enterobacterales</i> alone (63.6%). Using disk diffusion, 66.3% of all isolates were classified as susceptible to the antibiotic. <i>K. pneumoniae</i> isolates co-harboring NDM and OXA-48 were susceptible in 65.3% of cases, while NDM-only producers were resistant. All <i>P. aeruginosa</i> isolates tested were susceptible to the antibiotic. Susceptibility rates in <i>A. baumannii</i> were lower (68.8%), with variability between testing methods. <b>Conclusions</b>: 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.