Selection and molecular characterization of ceftazidime/avibactam-resistant mutants in Pseudomonas aeruginosa strains containing derepressed AmpC. (1st February 2015)

• Record Type: Journal Article
• Authors: Lahiri, Sushmita D.; Walkup, Grant K.; Whiteaker, James D.; Palmer, Tiffany; McCormack, Kathy; Tanudra, M. Angela; Nash, Tory J.; Thresher, Jason; Johnstone, Michele R.; Hajec, Laurie; Livchak, Stephania; McLaughlin, Robert E.; Alm, Richard A.
• Is Part Of: Journal of antimicrobial chemotherapy. Volume 70:Number 6(2015:Jun.)
• Page Start: 1650
• Page End: 1658
• Publication Date: 2015-02-01
• Subjects: extended-spectrum cephalosporinases -- ESAC -- Ω-loop -- cephalosporins; Anti-infective agents -- Periodicals; Chemotherapy -- Periodicals; 615.58
• DOI: 10.1093/jac/dkv004
• Languages: English
• ISSNs: 0305-7453

Abstract

Abstract: Objectives: Pseudomonas aeruginosa is an important nosocomial pathogen that can cause a wide range of infections resulting in significant morbidity and mortality. Avibactam, a novel non-β-lactam β-lactamase inhibitor, is being developed in combination with ceftazidime and has the potential to be a valuable addition to the treatment options for the infectious diseases practitioner. We compared the frequency of resistance development to ceftazidime/avibactam in three P. aeruginosa strains that carried derepressed ampC alleles. Methods: The strains were incubated in the presence of increasing concentrations of ceftazidime with a fixed concentration (4 mg/L) of avibactam to calculate the frequency of spontaneous resistance. The mutants were characterized by WGS to identify the underlying mechanism of resistance. A representative mutant protein was characterized biochemically. Results: The resistance frequency was very low in all strains. The resistant variants isolated exhibited ceftazidime/avibactam MIC values that ranged from 64 to 256 mg/L. All of the mutants exhibited changes in the chromosomal ampC gene, the majority of which were deletions of various sizes in the Ω-loop region of AmpC. The mutant enzyme that carried the smallest Ω-loop deletion, which formed a part of the avibactam-binding pocket, was characterized biochemically and found to be less effectively inhibited by avibactam as well as exhibiting increased hydrolysis of ceftazidime. Conclusions: The development of high-level resistance to ceftazidime/avibactam appears to occur at low frequency, but structural modifications in AmpC can occur that impact the ability of avibactam to inhibit the enzyme and thereby protect ceftazidime from hydrolysis.