Phytol derivatives as drug resistance reversal agents.

Phytol was chemically transformed into fifteen semi-synthetic derivatives, which were evaluated for their antibacterial and drug resistance reversal potential in combination with nalidixic acid against E. coli strains CA8000 and DH5α. The pivaloyl (4), 3,4,5-trimethoxybenzoyl (9), 2,3-dichlorobenzoyl (10), cinnamoyl (11), and aldehyde (14) derivatives of phytol ((2E,7R,11R)-3,7,11,15-tetramethyl-2-hexadecen-1-ol) were evaluated by using another antibiotic, tetracycline, against the MDREC-KG4 clinical isolate of E. coli. Derivative 4 decreased the maximal inhibitory concentration (MIC) of the antibiotics by 16-fold, while derivatives 9, 10, 11, and 14 reduced MIC values of the antibiotics up to eightfold against the E. coli strains. Derivatives 4, 9, 10, 11, and 14 inhibited the ATP-dependent efflux pump; this was also supported by their in silico binding affinity and down-regulation of the efflux pump gene yojI, which encodes the multidrug ATP-binding cassette transporter protein. This study supports the possible use of phytol derivatives in the development of cost-effective antibacterial combinations.