The mechanism of aminoglycoside resistance among 338 gentamicin-nonsusceptible Gram-negative bacteria (207 Enterobacteriaceae and 131 Pseudomonas aeruginosa) was assessed, and the in vitro activity of ceftazidime-avibactam against these isolates was determined. Aminoglycoside-modifying enzymes were detected in 91.8% of Enterobacteriaceae and 13.7% of P. aeruginosa isolates. A single strain of Klebsiella pneumoniae harbored a 16S rRNA methylase (ArmA). The ceftazidime-avibactam MIC90 values were 0.5 μg/ml (MIC, ≤8 μg/ml for 100% of isolates) and 16 μg/ml (MIC, ≤8 μg/ml for 87.8% of isolates) against gentamicin-nonsusceptible Enterobacteriaceae and P. aeruginosa isolates, respectively.
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