Objectives: To assess the in vitro antibacterial activity of ceftazidime/avibactam against a recent Italian collection
of carbapenem-resistant Enterobacterales (CRE) isolated from urine specimens.
Methods: Consecutive Gram-negative isolates from urine specimens, collected from inpatients in five Italian
hospitals during the period October 2016 to February 2017, were screened for CRE phenotype using chromogenic
selective medium and identified using MALDI-TOF MS. Antimicrobial susceptibility testing was performed by reference
broth microdilution (BMD) and, for ceftazidime/avibactam, also by EtestVR CZA. Results were interpreted
according to the EUCAST breakpoints. All confirmed CRE were subjected to real-time PCR targeting blaKPC-type,
blaVIM-type, blaNDM-type and blaOXA-48-type carbapenemase genes. Non-MBL-producing isolates resistant to ceftazidime/
avibactam were subjected toWGS and their resistome and clonality were analysed.
Results: Overall, 318 non-replicate presumptive CRE were collected following screening of 9405 isolates
of Enterobacterales (3.4%) on chromogenic selective medium. Molecular analysis revealed that 216 isolates
were positive for a carbapenemase gene (of which 92.1%, 2.8%, 1.4% and 1.4% were positive for blaKPC-type,
blaOXA-48-type, blaNDM-type and blaVIM-type, respectively). Against the confirmed carbapenemase-producing
Enterobacterales (CPE), ceftazidime/avibactam was the most active compound, followed by colistin (susceptibility rates 91.6% and 69.4%, respectively). Compared with BMD, EtestVR for ceftazidime/avibactam yielded
consistent results (100% category agreement). All class B b-lactamase producers were resistant to ceftazidime/
avibactam, while OXA-48 and KPC producers were susceptible, with the exception of seven KPC-producing isolates
(4.2%). The latter exhibited an MIC of 16 to >32 mg/L, belonged to ST512, produced KPC-3 and showed
alterations in the OmpK35 and Ompk36 porins.
Conclusions: Ceftazidime/avibactam showed potent in vitro activity against a recent Italian collection of CPE