Relebactam restores susceptibility of resistant Pseudomonas aeruginosa and Enterobacterales and enhances imipenem activity against chromosomal AmpC-producing species: analysis of global SMART 2018–2020

Background Carbapenem-resistant bacteria are an increasing problem in clinical practice; thus, it is important to identify β-lactamase inhibitors ( e.g. , relebactam) that can restore carbapenem susceptibility.

We report analyses of relebactam enhancement of imipenem activity against both imipenem-nonsusceptible (NS) and imipenem-susceptible (S) Pseudomonas aeruginosa and Enterobacterales.

Gram-negative bacterial isolates were collected for the ongoing Study for Monitoring Antimicrobial Resistance Trends global surveillance program.

Clinical and Laboratory Standards Institute–defined broth microdilution minimum inhibitory concentrations (MIC) were used to determine the imipenem and imipenem/relebactam antibacterial susceptibilities of P. aeruginosa and Enterobacterales isolates.

Results Between 2018 and 2020, 36.2% of P. aeruginosa ( N  = 23,073) and 8.2% of Enterobacterales ( N  = 91,769) isolates were imipenem-NS.

Relebactam restored imipenem susceptibility in 64.1% and 49.4% of imipenem-NS P. aeruginosa and Enterobacterales isolates, respectively.

Restoration of susceptibility was largely observed among K. pneumoniae carbapenemase-producing Enterobacterales and carbapenemase-negative P. aeruginosa .

Relebactam also caused a lowering of imipenem MIC among imipenem-S P. aeruginosa and Enterobacterales isolates from chromosomal Ambler class C β-lactamase (AmpC)–producing species.

For both imipenem-NS and imipenem-S P. aeruginosa isolates, relebactam reduced the imipenem MIC mode from 16 μg/mL to 1 μg/mL and from 2 μg/mL to 0.5 μg/mL, respectively, compared with imipenem alone.

Conclusions Relebactam restored imipenem susceptibility among nonsusceptible isolates of P. aeruginosa and Enterobacterales and enhanced imipenem susceptibility among susceptible isolates of P. aeruginosa and isolates from Enterobacterales species that can produce chromosomal AmpC.

The reduced imipenem modal MIC values with relebactam may result in a higher probability of target attainment in patients.