Molecular Characterization of Baseline and Pseudomonas aeruginosa Isolates from a Phase 3 Nosocomial Pneumonia (ASPECT-NP) Clinical Trial.

We reviewed β-lactam-resistant baseline species and lower respiratory tract isolates collected during the ASPECT-NP phase 3 clinical trial that evaluated the safety and efficacy of ceftolozane-tazobactam compared with meropenem for the treatment of nosocomial pneumonia in ventilated adults. Isolates were subjected to whole-genome sequencing, real-time PCR for the quantification of the expression levels of β-lactamase and efflux pump genes, and Western blot analysis for the detection of OprD ( only). Extended-spectrum β-lactamase (ESBL) genes were detected in 168 of 262 isolates, and among these, was the most common, detected in 125 isolates. Sixty-one isolates carried genes encoding carbapenemases, while 33 isolates did not carry ESBLs or carbapenemases. Carbapenemase-producing isolates carried mainly NDM and OXA-48 variants, with ceftolozane-tazobactam MIC values ranging from 4 to 128 µg/ml. Most ceftolozane-tazobactam-nonsusceptible isolates that did not carry carbapenemases were isolates that exhibited disrupted OmpK35, specific mutations in OmpK36, and, in some isolates, elevated expression of Among 89 isolates, carbapenemases and ESBL-encoding genes were observed in 12 and 22 isolates, respectively. isolates without acquired β-lactamases displaying elevated expression of AmpC (14 isolates), elevated expression of efflux pumps (11 isolates), and/or a decrease or loss of OprD (22 isolates) were susceptible to ceftolozane-tazobactam. Ceftolozane-tazobactam was active against >75% of the isolates from the ASPECT-NP trial that did not carry carbapenemases. strains resistant to ceftolozane-tazobactam might represent a challenge for treatment due to their multiple resistance mechanisms. Ceftolozane-tazobactam was among the agents that displayed the greatest activity against isolates. (This study has been registered at ClinicalTrials.gov under registration no. NCT02070757.).