Restoring colistin sensitivity in colistin-resistant gram-negative bacteria: combinatorial use of α-terpineol and colistin

Multidrug-resistant gram-negative bacteria (GNB) have posed a serious public health hazard worldwide. Colistin (COL), the ultimate therapeutic option for treating GNB infections, has had escalating resistance rates concomitant with increased utilization. In this study, we attempted to increase the sensitivity to COL using a plant extract, α-terpineol (α-TP). Checkerboard and time-kill assays indicated that the combination of COL and α-TP exhibited pronounced synergistic antimicrobial effects against colistin-resistant (COL-R) GNB in vitro. Biofilm assessments revealed that COL combined with α-TP effectively inhibited biofilm development and eliminated established biofilms. Scanning electron microscopy indicated substantial disruption of bacterial cell membranes after 6 h of combined treatment. Additionally, cytotoxicity and erythrocyte hemolysis assays confirmed that α-TP maintained a degree of safety at synergistic concentrations. Mechanistically, the combination of COL and α-TP promoted the accumulation of reactive oxygen species and enhanced the permeability of both the inner and outer bacterial membranes. This study demonstrated that α-TP can restore the sensitivity of COL-R GNB to COL when used in combination.