title: Reversal of efflux mediated antifungal resistance underlies synergistic activity of two monoterpenes with fluconazole.
abstract: Thymol (THY) and carvacrol (CARV), the principal chemical components of thyme oil have long been known for their wide use in medicine due to antimicrobial and disinfectant properties. This study, however, draws attention to a possible synergistic antifungal effect of these monoterpenes with azole antimycotic-fluconazole. Resistance to azoles in Candida albicans involves over-expression of efflux-pump genes MDR1, CDR1, CDR2 or mutations and over-expression of target gene ERG11. The inhibition of drug efflux pumps is considered a feasible strategy to overcome clinical antifungal resistance. To put forward this approach, we investigated the combination effects of these monoterpenes and FLC against 38 clinically obtained FLC-sensitive, and eleven FLC-resistant Candida isolates. Synergism was observed with combinations of THY-FLC and CARV-FLC evaluated by checkerboard microdilution method and nature of the interactions was calculated by FICI. In addition, antifungal activity was assessed using agar-diffusion and time-kill curves. The drug efflux activity was determined using two dyes, Rhodamine6G (R6G) and fluorescent Hoechst 33342. No significant differences were observed in dye uptakes between FLC-susceptible and resistant isolates, incubated in glucose free buffer. However, a significantly higher efflux was recorded in FLC-resistant isolates when glucose was added. Both monoterpenes inhibited efflux by 70-90%, showing their high potency to block drug transporter pumps. Significant differences, in the expression levels of CDR1 and MDR1, induced by monoterpenes revealed reversal of FLC-resistance. The selectively fungicidal characteristics and ability to restore FLC susceptibility in resistant isolates signify a promising candidature of THY and CARV as antifungal agents in combinational treatments for candidiasis.
authors.affiliation: Department of Biosciences, Jamia Millia Islamia, New Delhi 110 025, India.
authors.forename: Aijaz
authors.initials: A
authors.lastname: Ahmad
authors.forename: Amber
authors.initials: A
authors.lastname: Khan
authors.forename: Nikhat
authors.initials: N
authors.lastname: Manzoor
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics; D000935:Antifungal Agents / Q000008:administration & dosage*; D001562:Benzimidazoles / Q000378:metabolism; D002175:Candida / Q000187:drug effects* / Q000502:physiology; D000081007:Cymenes; D004357:Drug Synergism; D015725:Fluconazole / Q000008:administration & dosage*; D005456:Fluorescent Dyes / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D026901:Membrane Transport Proteins / Q000235:genetics; D008826:Microbial Sensitivity Tests; D039821:Monoterpenes / Q000008:administration & dosage*; D013943:Thymol / Q000008:administration & dosage*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000935:Antifungal Agents; D001562:Benzimidazoles; C094693:CDR1 protein, Candida albicans; D000081007:Cymenes; D005456:Fluorescent Dyes; D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D039821:Monoterpenes; D013943:Thymol; D015725:Fluconazole; C073316:carvacrol; C017807:bisbenzimide ethoxide trihydrochloride