Synergistic Activity of Colistin in Combination With Resveratrol Against Colistin-Resistant Gram-Negative Pathogens

Abstract

Objectives: In this study, we investigated the antimicrobial activity of resveratrol in combination with colistin, a last-resort agent for the treatment of severe infections caused by multidrug resistant Gram-negative pathogens. Methods: The synergistic activity and the bactericidal activity of colistin in combination with resveratrol was investigated by checkerboard assays and time-kill assays, respectively. A total of 21 strains were investigated, including 16 strains of different species (Klebsiella pneumoniae, n = 6, Escherichia coli, n = 6; Citrobacter braakii, n = 1; Stenotrophomonas malthophilia, n = 1; Enterobacter cloaceae, n = 1; Acinetobacter baumannii, n = 1) with acquired colistin resistance, three colistin-susceptible K. pneumoniae precursors, and two strains of intrinsically colistin-resistant species (Serratia marcescens, n = 1; Proteus mirabilis, n = 1). Mechanisms of acquired colistin resistance included chromosomal mutations (i.e., mgrB, pmrAB) and plasmid genes (mcr-1, mcr-1.2). Results: Resveratrol did not show any significant intrinsic antimicrobial activity. Overall, a relevant synergistic antimicrobial activity of resveratrol in combination with colistin was observed with all tested strains, except for the three colistin-susceptible K. pneumoniae strains, and for two mcr-1-positive E. coli strains. In time-kill assays, performed with 15 selected strains, the combination of colistin 2 mg/L plus resveratrol 128 mg/L was bactericidal with 11 strains, and bacteriostatic for the remaining ones. Conclusions: Resveratrol was found to potentiate colistin activity against a wide panel of colistin-resistant strains, regardless of species and resistance mechanisms, which would deserve further investigation for potential clinical applications.

Keywords: antibiotic resistance breakers; colistin; colistin resistance; combination therapy; resveratrol.

Figure 1

Time-kill assays with colistin 2 mg/L in combination with resveratrol 128 mg/L. Data are mean values from the results of two independent experiments, and the error bars represent standard deviations. The lowest number of CFU (detection limit) that can be detected by the method used is 1E+02 CFU/mL.

Figure 2

Time-kill assays with colistin at 0.5 or 1 X MIC in combination with resveratrol 128 mg/L, in the strains in which colistin 2 mg/L plus resveratrol 128 mg/L yielded a bacteriostatic effect. Data are mean values from the results of two independent experiments, and the error bars represent standard deviations. The lowest number of CFU (detection limit) that can be detected by the method used is 1E+02 CFU/mL.