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. Disclosures All authors: No reported disclosures. [ABSTRACT FROM AUTHOR]