Antimicrobial activity of ceftolozane-tazobactam tested against gram-negative contemporary (2015-2017) isolates from hospitalized patients with pneumonia in US medical centers.

Pseudomonas aeruginosa (n = 1531) and Enterobacteriaceae (n = 2373) clinical isolates from hospitalized patients with pneumonia were collected from 31 US medical centers during 2015-2017. Isolates were susceptibility tested against ceftolozane-tazobactam and comparators by broth microdilution. Results from intensive care unit (ICU) patients and patients with ventilator-associated bacterial pneumonia (VABP) were analyzed separately. Ceftolozane-tazobactam was very active against P. aeruginosa (MIC50/90 , 0.5/2 mg/L; 97.5% susceptible), including multidrug-resistant (87.9% susceptible) and extensively drug-resistant (82.9% susceptible). Ceftolozane-tazobactam inhibited 90.3% of Enterobacteriaceae isolates (MIC50/90 , 0.25/2 mg/L), including non-carbapenem-resistant Enterobacteriaceae isolates with an extended-spectrum β-lactamase phenotype (85.7% susceptible). Ceftolozane-tazobactam activity was stable against P. aeruginosa regardless of the US census division or ICU and VABP subsets (>90%); small differences were noted among Enterobacteriaceae isolates from the Middle Atlantic (range 78.3-88.9%) and West South Central (range 86.4-89.2%) divisions. These in vitro results indicate that ceftolozane-tazobactam may represent a valuable option for hospital-acquired bacterial pneumonia and VABP caused by Enterobacteriaceae and P. aeruginosa in the United States.