Institut d'Investigació Sanitària Illes Balears (IdISBa) Research Group.

In vitro evolution of cefepime/zidebactam (WCK 5222) resistance in Pseudomonas aeruginosa: dynamics, mechanisms, fitness trade-off and impact on in vivo efficacy

Isabel Barceló 1, Gabriel Cabot 1, Snehal Palwe 2, Prashant Joshi 2, Swapna Takalkar 2, Hariharan Periasamy 2, Sara Cortés-Lara 1, Laura Zamorano 1, Irina Sánchez-Diener 1, Bartolome Moya 1, Sachin Bhagwat 2, Mahesh Patel 2, Antonio Oliver 1

1 Servicio de Microbiología y Unidad de Investigación, Hospital Universitari Son Espases, Instituto de Investigación Sanitaria Illes Balears (IdISBa), Palma de Mallorca, Spain.
2 Wockhardt Research Centre, Aurangabad, India.


Objectives: To study the dynamics, mechanisms and fitness cost of resistance selection to cefepime, zidebactam and cefepime/zidebactam in Pseudomonas aeruginosa.

Methods: WT P. aeruginosa PAO1 and its ΔmutS derivative (PAOMS) were exposed to stepwise increasing concentrations of cefepime, zidebactam and cefepime/zidebactam. Selected mutants were characterized for change in susceptibility profiles, acquired mutations, fitness, virulence and in vivo susceptibility to cefepime/zidebactam. Mutations were identified through WGS. In vitro fitness was assessed by measuring growth in minimal medium and human serum-supplemented Mueller-Hinton broth. Virulence was determined in Caenorhabditis elegans and neutropenic mice lung infection models. In vivo susceptibility to a human-simulated regimen (HSR) of cefepime/zidebactam was studied in neutropenic mice lung infection.

Results: Resistance development was lower for the cefepime/zidebactam combination than for the individual components and high-level resistance was only achieved for PAOMS. Cefepime resistance development was associated with mutations leading to the hyperexpression of AmpC or MexXY-OprM, combined with PBP3 mutations and/or large chromosomal deletions involving galU. Zidebactam resistance was mainly associated with mutations in PBP2. On the other hand, resistance to cefepime/zidebactam required multiple mutations in genes encoding MexAB-OprM and its regulators, as well as PBP2 and PBP3. Cumulatively, these mutations inflicted significant fitness cost and cefepime/zidebactam-resistant mutants (MIC = 16-64 mg/L) remained susceptible in vivo to the HSR.

Conclusions: Development of cefepime/zidebactam resistance in P. aeruginosa required multiple simultaneous mutations that were associated with a significant impairment of fitness and virulence.

J Antimicrob Chemother. 2021 Sep 15;76(10):2546-2557. doi: 10.1093/jac/dkab213.

Link to J Antimicrob Chemother

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Dr. Bartolome Moyà

Instituto de Investigación Sanitaria Illes Balears

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