1436. Comparison of Ceftazidime–Avibactam, Ceftolozane–Tazobactam, Piperacillin–Tazobactam, and Meropenem Activities When Tested Against Gram-Negative Organisms Isolated From Complicated Urinary Tract Infections

BACKGROUND: Complicated urinary tract infections (cUTIs) represent a major cause of healthcare-associated infection and a major source of gram-negative (GN) bacteremia. We evaluated the antimicrobial activities of recently approved β-lactamase inhibitor combinations and comparators against GN bacteria isolated from patients with cUTIs in the US hospitals in 2018. METHODS: Unique patient isolates were consecutively collected from patients with cUTIs in 65 hospitals in 2018, and the GN organisms (n = 4,371) were susceptibility (S) tested by reference broth microdilution methods. Enterobacterales (ENT) with elevated cephalosporin MICs were screened for β-lactamase-encoding genes by whole-genome sequencing. RESULTS: The most common GN organisms were E. coli (44.5%), K. pneumoniae (19.6%), P. mirabilis (6.7%), and P. aeruginosa (PSA; 5.3%). The most active agents against ENT were ceftazidime–avibactam (CAZ-AVI; 99.9%S), amikacin (AMK; 99.7%S), and meropenem (MEM; 99.4%S; table). Extended-spectrum β-lactamase (ESBL) genes were identified in 315 ENT (7.6%; excluding carbapenemase co-producers), including CTX-M-15 (63% of ESBL producers), other CTX-M types (25%), OXA-1/OXA-30 (39%), and SHV type (30%); approximately 50% of ESBL producers had ≥2 ESBL genes, mainly a CTX-M-type and an OXA-type (37% of isolates). The most active agents against ESBL producers were CAZ-AVI (100.0%S), AMK (99.7%S), and MEM (99.4%S); whereas ceftolozane–tazobactam (C-T) and piperacillin–tazobactam (PIP-TAZ) were active against 90.6% and 84.8% of ESBL producers, respectively. Only CAZ-AVI (87.0%S), colistin (COL; 87.0%S), and tigecycline (95.7%S) exhibited good activity against carbapenem-resistant ENT (CRE). Only 3 ENT isolates (0.07%) were CAZ-AVI resistant and all had a metallo-β-lactamase gene (2 VIM-1 and 1 NDM-1). CAZ-AVI (97.0%S) and C-T (99.1%S) were the most active β-lactams tested against PSA; other compounds with > 90%S for PSA were COL (99.6%), AMK (97.8%), tobramycin (93.5%), and CAZ (90.4%). CONCLUSION: CAZ-AVI was highly active against a large collection of contemporary GN bacteria isolated from patients with cUTIs in US hospitals and provided greater coverage than the agents currently available in the US to treat cUTIs. [Image: see text] DISCLOSURES: All authors: No reported disclosures.