1589. Ceftolozane–Tazobactam Activity Against Difficult-to-Treat Resistance in Pseudomonas aeruginosa from Bloodstream Infections in US Hospitals

BACKGROUND: Infections caused by Pseudomonas aeruginosa (PSA) resistant to first-line agents are difficult to treat and require using more toxic antimicrobials, such as amikacin (AMK) and colistin (COL). Kadri et al. recently described the category of difficult-to-treat resistance (DTR) as intermediate or resistant to all tested first-line agents (fluoroquinolones, carbapenems, and extended-spectrum cephalosporins). Ceftolozane–tazobactam (C-T) is an antibacterial combination of an antipseudomonal cephalosporin and a β-lactamase inhibitor. C-T has been approved in >60 countries to treat complicated urinary tract infections, acute pyelonephritis, and complicated intra-abdominal infections. The filing is in progress for treatment of hospital-acquired pneumonia, including ventilator-associated pneumonia. The Program to Assess Ceftolozane–Tazobactam Susceptibility (PACTS) monitors gram-negative (GN) isolates resistant to C-T worldwide. In this study, the activity of C-T and comparators against PSA bloodstream isolates that are DTR, multidrug-resistant (MDR), or extensively drug-resistant (XDR) were analyzed. METHODS: A total of 922 PSA isolates from BSI were collected between 2011 and 2018 from 35 PACTS hospitals in the United States. Isolates were tested for C-T susceptibility (S) by the CLSI broth microdilution method. Other antibiotics tested included cefepime (FEP), ceftazidime (CAZ), ciprofloxacin, levofloxacin (LEV), doripenem, imipenem, meropenem (MEM), piperacillin–tazobactam (PIP-TAZ), AMK and COL. Antibiotic-resistant phenotypes analyzed using CLSI (2019) breakpoints included MDR (nonsusceptible to ≥ 1 agent in ≥ 3 drug classes), XDR (susceptible to ≤ 1 agent in ≤ 2 drug classes), or DTR. RESULTS: The percent of DTR isolates was 4.8% when compared with 15.2% MDR and 9.3% XDR. The %S for C-T and other first- and second-line agents are shown in the table for each phenotype. CONCLUSION: C-T demonstrated 97.1%S overall for BSI isolates, similar to AMK (97.8%) and COL (99.5%). C-T had better coverage than first-line drugs against MDR (81.4%) and XDR (72.1%), and 50% for the DTR isolates, which represented only 4.8% of isolates. Only AMK and COL had > 75%S for DTR isolates. [Image: see text] DISCLOSURES: All authors: No reported disclosures.