Antimicrobial Activity of Ceftazidime-Avibactam against Gram-Negative Bacteria Isolated from Patients Hospitalized with Pneumonia in U.S. Medical Centers, 2011 to 2015.

Bacterial isolates were collected from patients hospitalized with pneumonia (PHP), including ventilator-associated pneumonia (VAP), from 76 U.S. medical centers in 2011 to 2015. The Gram-negative organisms (n = 11,185, including 1,097 from VAP) were tested for susceptibility to ceftazidime-avibactam and comparators by the broth microdilution method. β-Lactamase-encoding genes were screened using a microarray-based assay on selected isolates. Pseudomonas aeruginosa and Klebsiella spp. were the most common Gram-negative bacteria isolated from PHP and VAP. Ceftazidime-avibactam was very active against P. aeruginosa (n = 3,402; MIC50/MIC90, 2 and 4 μg/ml; 96.6% susceptible), including isolates nonsusceptible to meropenem (86.3% susceptible to ceftazidime-avibactam), piperacillin-tazobactam (85.6% susceptible), or ceftazidime (80.6% susceptible). Ceftazidime-avibactam was also highly active against Enterobacteriaceae (MIC50/MIC90, 0.12 and 0.5 μg/ml; 99.9% susceptible), including carbapenem-resistant Enterobacteriaceae (CRE) (n = 189; MIC50/MIC90, 0.5 and 2 μg/ml; 98.0% susceptible) and multidrug-resistant (MDR) (n = 674; MIC50/MIC90, 0.25 and 1 μg/ml; 98.8% susceptible) and extensively drug-resistant (XDR) (n = 156; MIC50/MIC90, 0.5 and 2 μg/ml; 98.1% susceptible) Enterobacteriaceae isolates, as well as Klebsiella species isolates showing an extended-spectrum β-lactamase (ESBL) screening-positive phenotype (n = 433; MIC50/MIC90, 0.25 and 1 μg/ml; 99.5% susceptible). Among Enterobacter spp. (24.8% ceftazidime nonsusceptible), 99.8% of the isolates, including 99.4% of ceftazidime-nonsusceptible isolates, were susceptible to ceftazidime-avibactam. The most common β-lactamases detected among Klebsiella pneumoniae and E. coli isolates were K. pneumoniae carbapenemase (KPC)-like and CTX-M-15, respectively. Only 8 of 6,209 Enterobacteriaceae isolates (0.1%) were ceftazidime-avibactam nonsusceptible, three NDM-1-producing strains with ceftazidime-avibactam MIC values of >32 μg/ml and five isolates with ceftazidime-avibactam MIC values of 16 μg/ml and negative results for all β-lactamases tested. Susceptibility rates among isolates from VAP were generally similar or slightly higher than those from all PHP.