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Strategies to overcome intrinsic resistance in Stenotrophomonas maltophilia: In vitro activity of aztreonam/avibactam, cefiderocol, and cefepime–zidebactam

Ramesh V, Rathakrishnan B, Bakthavatchalam YD, Lal B, Manesh A, Shankar BA, Jayaprada R, Rajni E et al.

2026

Abstract

Abstract Purpose: To evaluate the in vitro activity of cefiderocol, aztreonam/avibactam, and cefepime/zidebactam against contemporary clinical Stenotrophomonas maltophilia isolates and to assess bactericidal activity using time-kill analyses.

Methods:: A total of 216 nonduplicate clinical S. maltophilia isolates collected between 2018 and 2024 from five tertiary care hospitals in India, were studied. MICs of trimethoprim/sulfamethoxazole (TMP-SMX), levofloxacin, minocycline, cefiderocol, aztreonam/avibactam, and cefepime/zidebactam were determined by broth microdilution according to CLSI guidelines. Cefiderocol was tested in iron-depleted cation-adjusted Mueller–Hinton broth. Aztreonam/avibactam was tested with avibactam at 4 mg/L, and cefepime/zidebactam at a 1:1 ratio. PK/PD breakpoints of ≤ 8 mg/L and ≤ 64 mg/L were applied for aztreonam/avibactam and cefepime/zidebactam, respectively. Time–kill assays were performed at 1× MIC against two representative isolates and ten additional isolates spanning cefepime/zidebactam MICs of 4–64 mg/L.

Results:: Cefiderocol inhibited 96.8% of isolates at MICs ≤ 1 mg/L (MIC50/MIC90 ≤ 0.12/1 mg/L). Susceptibility rates were 95.8% for aztreonam/avibactam and 99.5% for cefepime/zidebactam. TMP-SMX and levofloxacin each inhibited 91.7% of isolates, while minocycline susceptibility was 92.6%. The three novel agents retained activity against most isolates non-susceptible to comparators. In time–kill assays, cefiderocol, aztreonam/avibactam, and…

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