biostudies-literatureFraile-Ribot PAMinisterio de Economía, Industria y Competitividad, Gobierno de Españae0098621https://www.ebi.ac.uk/biostudies/studies/S-EPMC8370190biostudies-literatureUnknown65(9)The mechanisms underlying an <i>in vivo</i> switch in the resistance phenotype of P. aeruginosa after ceftazidime-avibactam treatment was investigated. The initial isolate (a blood culture) was resistant to meropenem but remained susceptible to antipseudomonal cephalosporins and combinations with β-lactamase inhibitors. One week after ceftazidime-avibactam therapy, a subsequent isolate (a rectal swab) recovered from the same patient showed the opposite phenotype. Whole-genome sequence analysis revealed a single SNP difference between both (ST235) isolates, leading to a P162S change in <i>bla</i>_GES-5, creating <i>bla</i>_GES-15. Thus, <i>bla</i>_GES-1, <i>bla</i>_GES-5, and <i>bla</i>_GES-15 were cloned and expressed in the wild-type straiAntimicrobial agents and chemotherapy<i>In Vivo</i> Evolution of GES β-Lactamases Driven by Ceftazidime/Avibactam Treatment of Pseudomonas aeruginosa Infections.PMC8370190RD16/0016PI18/00076PI21/00017Oliver AMulet XFernandez JGomis-Font MAForcelledo LLopez-Causape CFraile-Ribot PAfalse<i>In Vivo</i> Evolution of GES β-Lactamases Driven by Ceftazidime/Avibactam Treatment of Pseudomonas aeruginosa Infections.The mechanisms underlying an <i>in vivo</i> switch in the resistance phenotype of P. aeruginosa after ceftazidime-avibactam treatment was investigated. The initial isolate (a blood culture) was resistant to meropenem but remained susceptible to antipseudomonal cephalosporins and combinations with β-lactamase inhibitors. One week after ceftazidime-avibactam therapy, a subsequent isolate (a rectal swab) recovered from the same patient showed the opposite phenotype. Whole-genome sequence analysis revealed a single SNP difference between both (ST235) isolates, leading to a P162S change in <i>bla</i>_GES-5, creating <i>bla</i>_GES-15. Thus, <i>bla</i>_GES-1, <i>bla</i>_GES-5, and <i>bla</i>_GES-15 were cloned and expressed in the wild-type strai2021-01-01T00:00:00Z2021 Aug2025-04-22T09:57:23.19Z2025-04-05T23:23:17.013ZS-EPMC83701903412559310.1128/aac.00986-2110.1128/AAC.00986-21