129. Antimicrobial Activity of Ceftazidime–avibactam and Comparator Agents Tested against Gram-Negative Organisms Isolated from Patients with Bloodstream Infections in United States Medical Centers (2017–2018)

BACKGROUND: We evaluated the antimicrobial susceptibility of Enterobacterales (ENT) and P. aeruginosa (PSA) causing bloodstream infections (BSIs) in the United States (US) hospitals. METHODS: A total of 3,317 ENT and 331 PSA isolates were consecutively collected (1/patient) from patients with BSI in 68 US medical centers in 2017–2018 and tested for susceptibility (S) by reference broth microdilution methods in a central laboratory as part of the International Network for Optimal Resistance Monitoring (INFORM) Program. β-Lactamase screening was performed by whole-genome sequencing on ENT with decreased S to broad-spectrum cephalosporins (ESBL phenotype). RESULTS: The most common ENT species isolated from BSI were E. coli (EC; 41.9% of ENT), K. pneumoniae (KPN; 24.4%), and E. cloacae (ECL; 8.7%), and the most active agents against ENT were ceftazidime–avibactam (CAZ-AVI; 99.9%S), amikacin (AMK; 99.6%S) and meropenem (MEM; 99.3%S). CAZ-AVI was active against all EC and KPN isolates (100.0%S). Only 2 ENT isolates (0.06%) were CAZ-AVI resistant, 2 NDM-1-producing ECL isolated in the New York City area. Ceftolozane–tazobactam (C-T) and piperacillin–tazobactam (PIP-TAZ) showed good activity against EC and KPN (92.2–98.9%S; Table), with limited activity against ECL (81.9–83.7%S). The most common ESBLs were CTX-M-type, which was observed in 93% of ESBL producers (mainly CTX-M-15 [64% of ESBL producers] and CTX-M-27 [13%]), and OXA-1/OXA-30 (42%); 42% of ESBL producers (n = 333, excluding carbapenemase producers) displayed ≥2 ESBL genes, mainly CTX-M-15 and OXA-1/OXA-30 (40% of ESBL producers). The most active agents against ESBL producers were CAZ-AVI (100.0%S), imipenem (99.4%S), and colistin (COL; 99.1%S). Only CAZ-AVI (99.4%S), AMK (96.2%S) and MEM (92.8%S) were active against >90% of multidrug-resistant (MDR) ENT. Among 19 carbapenem-resistant ENT (CRE; 0.6% of ENT), 9 produced a KPC-like, 2 an NDM-1, and 2 an NMC-A; carbapenemase genes were not found in 6 CRE isolates. COL (100.0%S), CAZ-AVI (98.5%S), AMK (98.5%S), C-T (98.1%S), and tobramycin (97.0%S) were very active against PSA. CONCLUSION: CAZ-AVI exhibited potent in vitro activity and great spectrum against ENT (99.9%S) and PSA (98.5%) isolated from patients with BSI from US hospitals. [Image: see text] DISCLOSURES: All authors: No reported disclosures.