In vitro activity of ceftazidime-avibactam against Gram-negative isolates collected in 18 European countries, 2015-2017.

Background: Between 2015-2017, 21 850 Enterobacterales isolates and 6156 Pseudomonas aeruginosa (P. aeruginosa) isolates were collected by 77 centers in 18 European countries as part of the International Network for Optimal Resistance Monitoring (INFORM) study (which was included into the Antimicrobial Testing Leadership and Surveillance [ATLAS] study in 2018).

Methods: A central reference laboratory performed antimicrobial susceptibility testing using broth microdilution panels according to Clinical and Laboratory Standards Institute guidelines. The presence of β-lactamases was confirmed using multiplex PCR assays.

Results: Among Enterobacterales isolates, the highest rates of susceptibility were to ceftazidime-avibactam (99.0%; MIC 0.5 mg/L), meropenem (96.3%), amikacin (95.2%), and imipenem (92.8%). All Enterobacterales organisms were highly susceptible to colistin (≥ 94.6%), apart from Proteus mirabilis, which is intrinsically resistant to colistin. Susceptibility rates among ceftazidime-resistant isolates were 95.7% for ceftazidime-avibactam and 87.9% for colistin, and 78.5% and 71.1%, respectively, among carbapenemase-positive isolates. Colistin was the only agent with activity against metallo-β-lactamases (100% susceptibility) among Enterobacterales and P. aeruginosa isolates. Overall susceptibility rates among P. aeruginosa were highest to colistin (99.5%) and ceftazidime-avibactam (92.3%), and were similar to ceftazidime-resistant isolates for colistin (98.9%) and reduced to 66.2% for ceftazidime-avibactam. Susceptibility rates among multidrug-resistant P. aeruginosa isolates were 98.9% to colistin and 71.7% to ceftazidime-avibactam.

Conclusions: Clinical isolates of Enterobacterales and P. aeruginosa collected from Europe, between 2015-2017, were highly susceptible to ceftazidime-avibactam, suggesting it is a useful alternative agent for patients whose treatment options may be limited. Persistent antimicrobial resistance requires continued surveillance and monitoring.