[Source: Journal of Antimicrobial Chemotherapy, full page: (LINK). Abstract, edited.]
Potentiation of imipenem by relebactam for Pseudomonas aeruginosa from bacteraemia and respiratory infections
Carolyne Horner, Shazad Mushtaq, David M Livermore, BSAC Resistance Surveillance Standing Committee
Journal of Antimicrobial Chemotherapy, dkz133, https://doi.org/10.1093/jac/dkz133
Published: 29 April 2019
Imipenem resistance in Pseudomonas aeruginosa most often entails loss of the ‘carbapenem-specific’ porin OprD; more rarely it reflects acquired carbapenemases. Loss of OprD only confers resistance to imipenem if AmpC β-lactamase is expressed, and we investigated whether this mechanism was overcome by relebactam, a developmental diazabicyclooctane β-lactamase inhibitor.
Consecutive P. aeruginosa isolates causing bacteraemia or hospital-onset lower respiratory tract infections were collected between 2014 and 2016 under the aegis of the BSAC Resistance Surveillance Programme. Imipenem MICs were determined centrally by BSAC agar dilution, with relebactam at a fixed concentration (4 mg/L).
For most imipenem-susceptible P. aeruginosa (726/759, 95.7%), the MICs of imipenem alone were 0.5–2 mg/L and were decreased 3- to 4-fold by addition of relebactam, as based on geometric means or modes. For most imipenem-resistant P. aeruginosa (82/92, 89%), imipenem MICs were 8–16 mg/L, and were reduced to 1–2 mg/L by relebactam. These patterns applied regardless of whether the isolates were susceptible to penicillins and cephalosporins or had phenotypes suggesting derepressed AmpC or up-regulated efflux. Imipenem MICs for five P. aeruginosa with MBLs remained high (≥16 mg/L) regardless of relebactam.
Potentiation of imipenem by relebactam was almost universal, in accordance with the view that endogenous pseudomonal AmpC ordinarily protects against this carbapenem to a small degree. Imipenem MICs were reduced to the current breakpoint, or lower, except for MBL producers. Potentiation was not compromised by derepression of AmpC or up-regulation of efflux.
Issue Section: ORIGINAL RESEARCH
Keywords: Antibiotics; Drugs Resistance; Pseudomonas aeruginosa; Imipenem; Relebactam.