(474) Antimicrobial Susceptibility of Gram-Negative Bacteria From ICU and Non-ICU Patients

Introduction: Aztreonam (ATM) is stable to the hydrolysis of MBLs, and avibactam (AVI) protects ATM from serine β-lactamases. We evaluated the activity of ATM-AVI and recently approved β-lactamase inhibitor combinations (BLI) and to compare the antimicrobial susceptibility patterns of Enterobacterales (ENT) and P. aeruginosa (PSA) from ICU and non-ICU patients.

Methods: Clinical isolates (1/patient) were consecutively collected from 72 USA medical centers in 2020-2022 and tested for susceptibility (S) at a central laboratory by broth microdilution. Results for 5,421 isolates (4,117 ENT and 1,304 PSA) from ICU patients were analyzed and compared to those of 20,649 isolates (17,879 ENT and 2,770 PSA) from non-ICU patients. Results were stratified by organism and infection type.

Results: ATM-AVI inhibited 100.0%/>99.9/% ENT and 100.0%/98.3% of carbapenem-resistant (R) ENT (CRE) from ICU/non-ICU patients at ≤8 mg/L, respectively. Among ENT from ICU/non-ICU, 9.2%/6.2% were multidrug-R (MDR) and 1.0%/0.4% were extensively drug-R (XDR). When ENT was stratified by infection type, MDR rates were higher among ICU isolates from all infection types except pneumonia, where MDR rates were 9.3%/11.5% for ICU/non-ICU. CRE rates were 1.9%/0.7% for ICU/non-ICU ENT. CRE S rates were 88.5%/82.9% for ceftazidime(CAZ)-AVI, 82.1%/81.2% for meropenem-vaborbactam (MEM-VAB), and 78.2%/72.6% for imipenem-relebactam (IMI-REL) among ICU/non-ICU isolates. ATM-AVI was active against 97.4% (38/39) of CAZ-AVI-R ENT and 100.0% (n=36) of MEM-VAB-non-S ENT. Among PSA from ICU/non-ICU patients, S rates were 96.3%/97.6% for CAZ-AVI, 97.2/98.4% for ceftolozane-tazobactam (TOL-TAZ), 97.1%/98.0% for IMI-REL, 77.8%/84.6% for piperacillin-tazobactam, and 76.9%/85.8% for MEM; ATM-AVI inhibited 78.0%/81.9%of PSA at ≤8 mg/L. MDR rates were 16.2%/12.7% among PSA from ICU/non-ICU patients.

Conclusions: In general, lower S rates were observed among ICU compared with non-ICU isolates, except among isolates from patients with pneumonia. ATM-AVI exhibited potent in vitro activity and spectrum against ENT from ICU and non-ICU patients, including CRE and isolates non-S to CAZ-AVI and/or MEM-VAB. CAZ-AVI, TOL-TAZ, and IMI-REL were the most active compounds against PSA and ATM-AVI showed spectrum comparable to PIP-TAZ and MEM against PSA from ICU patients.