Evaluation of Synergistic Effect of Combined Treatment with Linalool and Colistin on Multidrug-Resistant Acinetobacter baumannii to Expand Candidate for Therapeutic Option

Abstract

Background: Acinetobacter baumannii infection is a significant health problem worldwide due to increased drug resistance. The limited antimicrobial alternatives for the treatment of severe infections by multidrug-resistant A. baumannii (MDRAB) make the search for other therapeutic options more urgent. Linalool, the major oil compound in Coriandrum sativum, was recently found to have high antibacterial activity against A. baumannii. The purpose of this study was to investigate the synergistic effect of linalool and colistin combinations against MDRAB and extensively drug-resistant A. baumannii (XDRAB). Methods: A total of 51 strains of A. baumannii clinical isolates, consisting of 10 MDRAB and 41 XDRAB were tested. We determined the minimum inhibitory concentration (MIC) of linalool for the test strains using the broth microdilution method and searched for interactions using the time-kill assay. Results: The time-kill assay showed that the linalool and colistin combination displayed a high rate of synergy (92.1%) (by synergy criterion 2), a low rate of indifference (7.8%), and a high rate of bactericidal activity (74.5%) in the 51 clinical isolates of A. baumannii. The synergy rates for the linalool and colistin combination against MDRAB and XDRAB were 96% and 92.1%, respectively. No antagonism was observed for the linalool and colistin combination. Conclusions: The combination of linalool and colistin showed a high synergy rate, which may be beneficial for controlling MDRAB infections. Therefore, this combination is a good candidate for in vivo studies to assess its efficacy in the treatment of MDRAB infections.