Methods: 189 baseline PSA isolates (one per patient) were included (19 countries). Isolates met the β-lactamase MIC screening criteria, and displayed CAZ MIC ≥16 µg/mL and/or carbapenem MIC ≥8 µg/mL. Susceptibility (S) testing was centrally performed by CLSI methods. Isolates underwent microarray-based assay, PCR/sequencing for screening of ESBL and carbapenemases (CARB), and qRT-PCR for determination of chromosomal AmpC expression.
Results: Isolates showed low S rates for CAZ (30.7%S; MIC50/90, 32/>64 µg/mL), meropenem (30.2%S; MIC50/90, 8/>8 µg/mL) and piperacillin-tazobactam (28.8%S; MIC50/90, 64/>128 µg/mL). In all, 27.5% (52/189) of isolates were CAZ-AVI resistant (R) and 36.5% (19/52) of these carried metallo-β-lactamases; 12 isolates carried IMP alleles, which were detected in China (blaIMP-25), Czech Republic (blaIMP-7), Mexico (blaIMP-18 and -56), Ukraine (blaIMP-1) and Vietnam (blaIMP-26), while 2 blaVIM-1-carrying PSA were found in Ukraine and 5 blaVIM-2 in Romania and Russia. Among CAZ-nonS PSA (69.3%; 131/189), 45.8% (60/131) showed overexpression of AmpC with or without blaOXA-like (OXA-2, -10 or -17), PSE-1, PER-1, IMP-56 or VIM-like (VIM-1 or -2) enzymes, 31.3% (41/131) had numerous combinations of CARB and ESBL enzymes, and 22.9% (30/131) had no β-lactamase genes detected. A total of 58/189 (30.7%) CAZ-S PSA were selected due to high MIC results for carbapenems. Among these 58 isolates, only 5 carried ESBL genes (blaOXA-2, blaPSE-1 and blaOXA-74).
Conclusion: A great proportion (45.8%) of CAZ-nonS PSA were hyper-producers of the chromosomal AmpC enzyme. CAZ-nonS isolates also carried various combinations of CARB and ESBL genes, while CAZ-S and carbapenem-R PSA likely had non-enzymatic β-lactam resistance mechanisms.
Funding: This study was sponsored by AstraZeneca (AZ). The AZ product ceftazidime-avibactam was acquired by Pfizer in December 2016.
R. E. Mendes,
L. N. Woosley, AstraZeneca: Research Contractor , Research grant
G. G. Stone, AstraZeneca: Formerly an employee and shareholder at time of study , salary and shareholder
Pfizer Inc.: Employee , Salary
R. Mclaughlin, AstraZeneca: Employee , Salary
P. Bradford, AstraZeneca: Formerly an employee and shareholder at time of study , salary and shareholder
R. K. Flamm, AstraZeneca: Research Contractor , Research grant