2427. Comparison of Ceftazidime–Avibactam and Ceftolozane-Tazobactam In Vitro Activities When Tested Against Gram-Negative Bacteria Isolated From Patients Hospitalized With Pneumonia in US Medical Centers (2017)

Background We evaluated Enterobacteriaceae (ENT) and P. aeruginosa (PSA) antimicrobial susceptibility patterns isolated from patients with pneumonia, including ventilator-associated pneumonia (VAP), and compared the in vitro activity of ceftazidime–avibactam (CAZ-AVI) and ceftolozane–tazobactam (C-T) against various-resistant (R) subsets. Methods Clinical isolates consecutively collected (1/patient) from 70 US medical centers in 2017 by the INFORM Program were susceptibility (S) tested against CAZ-AVI, C-T, and comparators at a central laboratory by reference broth microdilution methods. The organism collection included 1,865 ENT and 1,337 PSA isolates. Results The most active agents against ENT were CAZ-AVI (99.9%S; table), amikacin (AMK; 98.7%S), the carbapenems meropenem (MEM) and doripenem (97.3%S), and tigecycline (TGC; 94.1%S), but only CAZ-AVI and TGC retained good activity (≥90%S) against carbepenem-R ENT (CRE; 98.0% and 90.0%S, respectively). The most active agents against multidrug-R (MDR) ENT were CAZ-AVI (99.6%S) and AMK (90.6%S), whereas C-T and MEM were active against only 55.2% and 77.7% of these organisms, respectively. CAZ-AVI was the most active agent tested against extensively drug-R (XDR) ENT (97.6%S) followed by AMK (73.2%S) and TGC (65.9%S). Among Klebsiella spp. with an ESBL phenotype, S to CAZ-AVI, C-T and MEM were 100.0%, 68.4%, and 83.9%, respectively. CAZ-AVI and C-T were very active against PSA and exhibited similar coverage against these organisms (96.2%S and 96.5%S, respectively), including MEM-non-S (NS; 88.1%S and 89.4%S), MDR (84.9%S and 86.4%S), and XDR (79.4%S and 80.4%S) isolates (table). Among PSA isolates NS to CAZ, MEM and piperacillin–tazobactam (P-T), S to CAZ-AVI, C-T, and AMK were 73.7%, 76.6% and 82.6%, respectively. All PSA isolates were colistin-S. Among isolates from VAP, S to CAZ-AVI and C-T were 100.0% and 90.2% for ENT (n = 266), and 97.8% and 99.5% for PSA (n = 183), respectively. Conclusion CAZ-AVI and C-T showed similar coverage (%S) against PSA (96.2–96.5%S), including against MDR (84.9–86.4%S) and XDR (79.4–80.4%S) isolates. In contrast, C-T was less active than CAZ-AVI against ENT in general and exhibited limited activity against ENT-R subsets. Disclosures H. S. Sader, Allergan: Research Contractor, Research support. R. K. Flamm, Allergan: Research Contractor, Research support. M. Castanheira, Allergan: Research Contractor, Research support.