Background: We evaluated Enterobacteriaceae (ENT) and P. aeruginosa (PSA) antimicrobial susceptibility patterns isolated from patients with pneumonia, including ventilator-associated pneumonia (VAP), and compared the in vitro activity of ceftazidime-avibactam (CAZ-AVI) and ceftolozane-tazobactam (C-T) against various resistant (R) subsets.
Methods: Clinical isolates consecutively collected (1/patient) from 70 US medical centers in 2017 by the INFORM Program were susceptibility (S) tested against CAZ-AVI, C-T, and comparators at a central laboratory by reference broth microdilution methods. The organism collection included 1,865 ENT and 1,337 PSA isolates.
Results: The most active agents against ENT were CAZ-AVI (99.9%S; Table), amikacin (AMK; 98.7%S), the carbapenems meropenem (MEM) and doripenem (97.3%S), and tigecycline (TGC; 94.1%S), but only CAZ-AVI and TGC retained good activity (≥90%S) against carbepenem-R ENT (CRE; 98.0% and 90.0%S, respectively). The most active agents against multidrug-R (MDR) ENT were CAZ-AVI (99.6%S) and AMK (90.6%S), whereas C-T and MEM were active against only 55.2% and 77.7% of these organisms, respectively. CAZ-AVI was the most active agent tested against extensively drug-R (XDR) ENT (97.6%S) followed by AMK (73.2%S) and TGC (65.9%S). Among Klebsiella spp. with an ESBL phenotype, S to CAZ-AVI, C-T and MEM were 100.0%, 68.4%, and 83.9%, respectively. CAZ-AVI and C-T were very active against PSA and exhibited similar coverage against these organisms (96.2%S and 96.5%S, respectively), including MEM-non-S (NS; 88.1%S and 89.4%S), MDR (84.9%S and 86.4%S), and XDR (79.4%S and 80.4%S) isolates (Table). Among PSA isolates NS to CAZ, MEM and piperacillin-tazobactam (P-T), S to CAZ-AVI, C-T, and AMK were 73.7%, 76.6% and 82.6%, respectively. All PSA isolates were colistin-S. Among isolates from VAP, S to CAZ-AVI and C-T were 100.0% and 90.2% for ENT (n=266), and 97.8% and 99.5% for PSA (n=183), respectively.
Conclusion: CAZ-AVI and C-T showed similar coverage (%S) against PSA (96.2-96.5%S), including against MDR (84.9-86.4%S) and XDR (79.4-80.4%S) isolates. In contrast, C-T was less active than CAZ-AVI against ENT in general and exhibited limited activity against ENT-R subsets.
H. S. Sader,
M. Castanheira, Allergan: Research Contractor , Research support .