2214. Comparison of Cefepime–Zidebactam (WCK 5222), Ceftazidime–Avibactam, and Ceftolozane–Tazobactam Tested Against Gram-Negative Organisms Causing Pneumonia in United States Hospitals in 2018

BACKGROUND: Zidebactam (ZID) is a bicyclo-acyl hydrazide antibiotic with a dual mechanism of action: selective Gram-negative PBP2 binding and β-lactamase inhibition. We evaluated the frequency and antimicrobial susceptibility (S) of Gram-negative bacilli (GNB) isolated from patients with pneumonia in US hospitals. METHODS: All 3,086 clinical isolates were consecutively collected from patients hospitalized with pneumonia (1/patient) in 29 US medical centers in 2018, and the GNB (n = 2,171) were S tested against cefepime (FEP)-ZID (1:1 ratio) and comparators by reference broth microdilution methods. The FEP S breakpoint of ≤8 mg/L (CLSI, high dose) was applied to FEP-ZID for comparison purposes. An FEP-ZID S breakpoint of ≤64 mg/L has been proposed for non-fermentative GNB based on pharmacokinetic/pharmacodynamic target attainment and was applied. Enterobacterales (ENT) isolateswere screened for β-lactamase genes by whole-genome sequencing. RESULTS: GNB represented 70.3% of the collection, and the most common GNB were P. aeruginosa (PSA; 34.9% of GNB), K. pneumoniae (10.9%), E. coli (9.7%), S. marcescens (7.7%), and S. maltophilia (XM; 6.4%). FEP-ZID was highly active against PSA (MIC(50/90), 2/8 mg/L; 98.8% and 99.9% inhibited at ≤8 and ≤16 mg/L, respectively; highest MIC, 32 mg/L), including resistant subsets (table). Among comparators, colistin (99.6%S), ceftazidime–avibactam (CAZ-AVI; 95.2%S), and ceftolozane–tazobactam (C-T; 94.5%S) were the most active compounds against PSA. FEP-ZID inhibited all ENT at ≤4 mg/L, including ESBL-producers (MIC(90), 0.25 mg/L) and carbapenem-resistant ENT (MIC(90), 4 mg/L). The most active comparators against ENT were CAZ-AVI (99.9%S), amikacin (98.5%S), and meropenem (MEM; 98.3%S). FEP-ZID inhibited 75.0% and 97.9% of XM isolates at ≤8 and ≤16 mg/L, respectively (highest MIC, 64 mg/L). The only other compounds active against XM were co-trimoxazole (MIC(50/90), ≤0.12/2 mg/L; 95.7%S) and levofloxacin (MIC(50/90), 1/2 mg/L; 70.7%S). FEP-ZID inhibited 71.0% and 98.9% of A. baumannii isolates at ≤8 and ≤64 mg/L,, respectively. CONCLUSION: FEP-ZID showed potent in vitro activity against GNB causing pneumonia in US hospitals and may represent a valuable therapeutic option for these difficult-to-treat infections [Image: see text] DISCLOSURES: All authors: No reported disclosures.