Objective: Stenotrophomonas maltophilia is a bacterium that presents challenges in treatment due to its resistance to numerous antibiotics. This study aimed to assess the in vitro susceptibility of trimethoprim/ sulfamethoxazole (TMP-SXT) and cefiderocol in S. maltophilia strains isolated as infectious agents following the clinical cut-off values established by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) and the Clinical & Laboratory Standards Institute (CLSI).

Methods: The study included 42 S. maltophilia strains identified as the causative agents of infection, with the initial isolate from each patient included in the analysis. Bacteria obtained from clinical specimens were identified using MALDI-TOF MS (Biotyper® sirius System, Bruker, Germany). Susceptibilities of isolates to TMPSXT and cefiderocol were tested using disc diffusion method. The results of antibiotic susceptibility test were evaluated according to EUCAST and CLSI guidelines.

Results: Of the patients, 16.7% had haematological malignancy and 83.7% had solid organ tumours. Of the patients, 21 (50%) were hospitalised in intensive care unit, 13 (31%) in surgical wards, 6 (14.3%) in internal wards and 2 (4.8%) in bone marrow unit. 4 (9.5%) of the bacteria were isolated from blood, 7 (16.7%) from urine, 7 (16.7%) from abscess and 24 (57.1%) from deep tracheal aspirate samples. According to EUCAST, all isolates were dose-dependent susceptible to TMP-SXT and susceptible to cefideroxol. According to CLSI, 14 (33.3%) isolates were dose-dependently susceptible, 28 (66.7%) were susceptible to TMP-SXT and all isolates were susceptible to cefiderocol. Zone diameters for cefiderocol were between 22-37mm. Conclusion: Cefiderocol is considered a suitable alternative for the treatment of infections caused by S. maltophilia. However, local epidemiological data should be utilized to monitor the emergence of resistance.