Spectrum of cefepime-taniborbactam coverage against 190 β-lactamases defined in engineered isogenic <i>Escherichia coli</i> strains

Cefepime-taniborbactam is a β-lactam/β-lactamase inhibitor combination in clinical development for the treatment of Enterobacterales and <i>Pseudomonas</i> infections, including carbapenem-resistant Enterobacterales and multidrug-resistant <i>Pseudomonas aeruginosa</i>. Taniborbactam is a novel cyclic boronate with direct inhibitory activity against clinically relevant Ambler class A, B, C, and D β-lactamases. To further characterize the spectrum of β-lactamase coverage by cefepime-taniborbactam, we constructed 190 isogenic strains of <i>Escherichia coli</i> that constitutively expressed a different β-lactamase. Synthetic codon-optimized genes encoding the mature periplasmic protein linked to the TEM-1 signal sequence were used for optimized expression and periplasmic localization of the β-lactamase. The repertoire of β-lactamases consisted of 50 Ambler class A, 34 class B (metallo), 48 class C, and 58 class D enzymes known to mediate β-lactam resistance in the clinical isolates of Enterobacterales and <i>P. aeruginosa</i>. Overall, in the 190 isogenic strains, the MIC₅₀/MIC₉₀ values were 8/128 µg/mL for cefepime and >128/>128 µg/mL for ceftazidime. Cefepime-taniborbactam (MIC₅₀/MIC₉₀ of 0.25/8 µg/mL) showed greater activity than ceftazidime-avibactam (MIC₅₀/MIC₉₀ of 4/>128 µg/mL) and similar activity to aztreonam-avibactam (MIC₅₀/MIC₉₀ of 0.5/4 µg/mL). Cefepime-taniborbactam inhibited strains overproducing metallo-β-lactamases, including clinically important NDM and VIM enzymes, whereas ceftazidime-avibactam showed no coverage. Among the 129 β-lactamase-overproducing strains with increased cefepime MIC ≥16-fold relative to the control strain, taniborbactam potentiated cefepime MIC by ≥8-fold for 113 strains overexpressing β-lactamases (42 Ambler class A, 24 B, 23 C, and 24 D). Cefepime-taniborbactam demonstrated broader activity relative to ceftazidime-avibactam and comparable activity with aztreonam-avibactam in the overall coverage of both serine- and metallo-β-lactamases from all four Ambler classes.