Impact of novel β-lactams on Gut Decolonization in Haematological Patients with Multidrug-Resistant Gram-Negative Infections

INTRODUCTION: Gut colonization by multidrug-resistant gram-negative bacilli (MDR-GNB) is a common precursor to bacteraemia in haematological patients with malignancies. This study evaluates the efficacy of ceftazidime/avibactam (CAZ/AVI) and ceftolozane/tazobactam (C/T) in eradicating gut MDR-GNB colonization. METHODS: This retrospective cohort included haematologic patients admitted to a tertiary hospital (2020-2023), colonized with carbapenem-resistant Enterobacterales or difficult-to-treat resistant (DTR) Pseudomonas aeruginosa and treated with CAZ/AVI or C/T. Decolonization was defined as clearance of baseline MDR-GNB in two consecutive post-treatment rectal swabs. RESULTS: Twenty treatment episodes were analysed. At the first post-treatment rectal swab, the previously identified colonizing MDR-GNB was not detected in 15/20 episodes (75.0%). The same colonizing MDR-GNB was re-identified in 3/15 cases (20.0%) on subsequent rectal swabs after a median of 8.0 days (IQR 7.5-11.0). Overall, 12/20 episodes (60.0%) achieved decolonization. Median follow-up was 327.0 days (IQR 225.0-480.8); sustained decolonization (≥180 days of follow-up) was documented in 9 episodes, while 5/12 episodes (41.7%) were recolonized with a different MDR-GNB. Among the eight episodes that remained colonized post-treatment, seven involved