In vitro sulbactam/avibactam synergy against carbapenem-resistant Acinetobacter baumannii from hospitals in Peru.

Objectives: To evaluate the synergistic activity of ampicillin/sulbactam plus ceftazidime/avibactam in a collection of carbapenem-resistant Acinetobacter baumannii (CR-Ab) from different regions in Peru. Materials and methods: One hundred and eighty-four CR-Ab isolates were included in this study. They were identified by amplification of bla OXA-51 and confirmed by MALDI-TOF (matrix-assisted laser desorption ionization time of flight) mass spectrometry and 16S rRNA sequencing. Susceptibility to ampicillin/sulbactam and carbapenems was determined by the disc diffusion method. Synergy was assessed using discs containing ampicillin/sulbactam and ceftazidime/avibactam. The EDTA-disc synergy test was used to screen metallo-β-lactamase-producing isolates, and in isolates showing synergy, the presence of bla NDM was confirmed by PCR. Statistical analysis was performed using Fisher's exact test. Results: High levels of resistance to ampicillin/sulbactam were found in the study. Thus, 1.1% (2/184), 11.4% (21/184) and 87.5% (161/184) of isolates were classified as susceptible, intermediate and resistant to ampicillin/sulbactam, respectively. Synergistic activity was observed in 97.2% of the non-susceptible CR-Ab isolates. The presence of metallo-β-lactamase producers (all bla NDM) was observed in three isolates (1.6%). Conclusions: These findings demonstrate high levels of synergistic activity between ampicillin/sulbactam and ceftazidime/avibactam and their potential use as a treatment for CR-Ab.