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Purpose Infections caused by resistant Gram-negative bacteria are becoming increasingly common and now pose a serious public health threat worldwide, because they are difficult to treat due to few treatment options and they are associated with high morbidity and mortality. The combination of ceftazidime with the beta-lactamase inhibitor avibactam – seems to be the right choice in this situation. The aim of the study was to evaluate the activity of ceftazidime/avibactam and other commonly used antibiotics against Enterobacterales and Pseudomonas aeruginosa strains isolated within last years in Poland. Patients and Methods This study analyzed the antibiotic susceptibility of 1607 Enterobacterales isolates and 543 nonfermenting P. aeruginosa strains collected between 2015 and 2019 in 4 medical laboratories participating in the ATLAS (Antimicrobial Testing Leadership And Surveillance) program in Poland. Unduplicated clinically significant Enterobacterales and P. aeruginosa strains were collected from patients with respiratory, skin and musculoskeletal, genitourinary, abdominal, bloodstream or other infections (ear, eye). Results The ceftazidime/avibactam combination demonstrates the highest activity against Enterobacterales (98.9%), in both adults and children, including strains presenting MDR (multidrug-resistant) (97.5%) and ESBL (extended spectrum β-lactamase) (96.3%) phenotypes. The activity of ceftazidime/avibactam increased to 100% when only MBL (metallo-β-lactamase)-negative subset of Enterobacterales was considered. This combination also achieved the second highest activity result (89.3%) after colistin in P. aeruginosa , including isolates of MDR (65.9%) and carbapenem-resistant (CR) phenotypes (54.8%). When MBL-positive isolates were excluded, susceptibility rate of P. aeruginosa increased to 94.7%. It is worth to note that susceptibility of the examined P. aeruginosa strains to ceftazidime/avibactam was very high in children (93.3%), especially in a pediatric intensive care unit (94.2%). Conclusion Enterobacterales and P. aeruginosa included in this analysis presented high susceptibility rates to ceftazidime/avibactam. Ceftazidime/avibactam showed the highest activity against Enterobacterales strains among all antibiotics studied, both for the total population as well as for MDR phenotype and ESBL phenotype. Ceftazidime/avibactam also achieved the second highest activity result against P. aeruginosa strains (including MDR and CR phenotypes). These results are much higher when excluding MBL-positive isolates that exhibit intrinsic resistance to ceftazidime/avibactam.

Antimicrobial susceptibility of clinical isolates collected from sites in central Europe in 2019 was tested by CLSI broth microdilution method and EUCAST breakpoints. Most active were amikacin, ceftazidime-avibactam and colistin; respectively, susceptibility rates among P. aeruginosa (n = 701) were 89.2%, 92.2% and 99.9%; difficult-to-treat (DTR) isolates, 62.5%, 37.5% and 100%; multidrug-resistant (MDR) isolates, 68.3%, 72.9% and 99.5%; meropenem-resistant (MEM-R), metallo-β-lactamase-negative (MBL-negative) isolates, 72.8%, 78.6% and 100%. Among Enterobacterales (n = 1639), susceptibility to ceftazidime-avibactam, colistin and tigecycline was ≥ 97.9%; MDR Enterobacterales, 96.8%, 94.4% and 100%, respectively; DTR isolates, ≥ 76.2% to ceftazidime-avibactam and colistin; MEM-R, MBL-negative isolates, ≥ 90.0% to ceftazidime-avibactam and colistin.