Evaluation of anti-Candida potential of geranium oil constituents against clinical isolates of Candida albicans differentially sensitive to fluconazole: inhibition of growth, dimorphism and sensitization

Abstract

Fluconazole (FLC) susceptibility of isolates of Candida spp., (n = 42) and efficacy as well as mechanism of anti-Candida activity of three constituents of geranium oil is evaluated in this study. No fluconazole resistance was observed among the clinical isolates tested, however 22% were susceptible-dose-dependent (S-DD) [minimal inhibitory concentration (MIC) ≥ 16 μg ml(-1)] and a standard strain of C. albicans ATCC 10231 was resistant (≥ 64 μg ml(-1)). Geraniol and geranyl acetate were equally effective, fungicidal at 0.064% v/v concentrations i.e. MICs (561 μg ml(-1) and 584 μg ml(-1) respectively) and killed 99.9% inoculum within 15 and 30 min of exposures respectively. Citronellol was least effective and fungistatic. C. albicans dimorphism (Y → H) was highly sensitive to geranium oil constituents tested (IC50 approximately 0.008% v/v). Geraniol, geranyl acetate and citronellol brought down MICs of FLC by 16-, 32- and 64-fold respectively in a FLC-resistant strain. Citronellol and geraniol arrested cells in G1 phase while geranyl acetate in G2-M phase of cell cycle at MIC(50). In vitro cytotoxicity study revealed that geraniol, geranyl acetate and citronellol were non-toxic to HeLa cells at MICs of the C. albicans growth. Our results indicate that two of the three geranium oil constituents tested exhibit excellent anti-Candida activity and significant synergistic activity with fluconazole.

Effects of Cinnamaldehyde, Ocimene, Camphene, Curcumin and Farnesene on <i>Candida albicans</i>

“…Camphene also reported to exhibit antioxidant, antinociceptive, antibacterial, expectorant, broncholytic, antiulcer activity and also helpful in expulsion of urolithiasis [41]- [50]. Ocimene, farnesene and camphene could be inhibiting C. albicans growth by affecting membrane integrity as terpenoids are known to cause cell wall and membrane damage [14] [15] [21]- [25]. However inhibition of sterol biosynthesis could also be associated with anti-Candida activity of camphene [50].…”

“…Plant molecules showed synergistic activity with antibiotics against bacterial and fungal pathogens and mechanisms of synergy was reported to be associated with enhancing penetration and bioavailability of antibiotics [12] [14] [15]. All the five plant molecules tested, exhibited excellent synergy with FLC against planktonic and biofilm growth of a recalcitrant strain of C. albicans (ATCC 10231) [28].…”

“…Anti-morphogenic activity supports membrane integrity damage (by terpenoids and cinnamaldehyde) mediated inhibition as it led to inhibition of morphogenesis through modulation of signaling pathways involved [7] [12] [14] [15] [17]- [24]. Curcumin is reported to up regulate TUP1, a negative regulator of hypahe induction [20] [51].…”

“…Time dependant killing of a Fluconazole resistant strain of C. albicans ATCC10231 inoculum by MFCs of ocimene and cinnamaldehyde was studied as done previously by Zore et al [14] [15]. In brief, C. albicans cells (2.5 × 10 3 cfu/ml) in 100 µl YPD broth, were exposed to MFCs of ocimene and cinnamaldehyde for different time intervals viz.…”

“…Effect of all the five plant molecules on serum induced morphogenesis of C. albicans (ATCC 10231) was studied by using micro titer plate based morphological assay as done previously by Zore et al [14] [15]. In brief, 100 µl of YPD supplemented with 25% horse serum and 24 h grown C. albicans yeast phase cells (10 5 cfu/ml), were treated with different concentrations of plant molecules viz.…”