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Characterization of Pseudomonas aeruginosa resistance to ceftolozane-tazobactam due to ampC and/or ampD mutations observed during treatment using semi-mechanistic PKPD modeling

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Deroche, Luc | Aranzana-Climent, Vincent | Rozenholc, Albane | Prouvensier, Laure | Darnaud, Léa | Grégoire, Nicolas | Marchand, Sandrine | Ploy, Marie-Cécile | François, Bruno | Couet, William | Barraud, Olivier | Buyck, Julien

Edité par CCSD ; American Society for Microbiology -

International audience. A double ampC (AmpC G183D ) and ampD (AmpD H157Y ) genes mutations have been identified by whole genome sequencing in a Pseudomonas aeruginosa (PaS) that became resistant (PaR) in a patient treated by ceftolozane/tazobactam (C/T). To precisely characterize the respective contributions of these mutations on the decreased susceptibility to C/T and on the parallel increased susceptibility to imipenem (IMI), mutants were generated by homologous recombination in PAO1 reference strain (PAO1- AmpC G183D , PAO1-AmpD H157Y , PAO1-AmpC G183D /AmpD H157Y ) and in PaR (PaR-AmpC PaS /AmpD PaS ). Sequential time-kill curve experiments were conducted on all strains and analyzed by semi-mechanistic PKPD modeling. A PKPD model with adaptation successfully described the data, allowing discrimination between initial and time-related (adaptive resistance) effects of mutations. With PAO1 and mutant-derived strains, initial EC 50 values increased by 1.4, 4.1, and 29-fold after AmpC G183D , AmpD H157Y and AmpC G183D /AmpD H157Y mutations, respectively. EC 50 values were increased by 320, 12.4, and 55-fold at the end of the 2 nd experiment. EC 50 of PAO1-AmpC G183D /AmpD H157Y was higher than that of single mutants at any time of the experiments. Within the PaR clinical background, reversal of AmpC G183D , and AmpD H157Y mutations led to an important decrease of EC 50 value, from 80.5 mg/L to 6.77 mg/L for PaR and PaR-AmpC PaS /AmpD PaS , respectively. The effect of mutations on IMI susceptibility mainly showed that the AmpC G183D mutation prevented the emergence of adaptive resistance. The model successfully described the separate and combined effect of AmpC G183D and AmpD H157Y mutations against C/T and IMI, allowing discrimination and quantification of the initial and time-related effects of mutations. This method could be reproduced in clinical strains to decipher complex resistance mechanisms.

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