Background: Ceftazidime-avibactam combination with aztreonam and role of rapid synergy reporting has not been widely evaluated. Also the synergy correlation with various betalactamases has not been widely studied.
Methods: We studied phenotypic synergy testings and molecular detection of betalactamases in our university hospital where we have large number of mellatobetalactmase producing bacteria. We tested two phenotypic synergy methods for ceftazidime-avibactam with aztreonam (Disc-E strip method, E strip-Agar method) for rapid reporting to clinicians (153 isolates). The treatment (colistin, ceftazidime-avibactam, ceftazidime-avibactam with aztreonam) was guided as indicated in the synergy testings. The resistance genes in bacteria were identified by polymerase chain reaction (PCR) and correlated with synergy results.
Results: The highest synergy was seen in Klebsiella pneumoniae by Disc-E strip and E strip-Agar method (86% and 84% respectively). About 70% of Pseudomonas aeruginosa and 29% of Escherichia coli showed synergy. Molecular methods revealed multiple resistance gene combinations and blaNDM (96%) was predominant gene in isolates showing synergy. Among isolates that were sensitive to ceftazidime-avibactam, the predominant genes were blaOXA-48 and blaIMP. Rapid laboratory reporting led to proper utilization of antibiotic combinations.
Conclusions: Ceftazidime-avibactam and aztreonam rapid synergy testing will be highly beneficial in treatment of infections by metallobetalactamase producing resistant bacteria, especially K. pneumoniae and P. aeruginosa.
Keywords: Synergy; aztreonam; ceftazidime–avibactam; clinical; phenotypic.