Antifungal activity of clotrimazole against Candida albicans depends on carbon sources, growth phase and morphology

Abstract

Vulvovaginal candidiasis, a superficial infection caused predominantly by the pathogenic fungus Candida albicans, is frequently treated with clotrimazole. Some drug formulations contain lactate for improved solubility. Lactate may modify C. albicans physiology and drug sensitivity by serving as a carbon source for the fungus and/or affecting local pH. Here, we explored the effects of lactate, in combination with pH changes, on C. albicans proliferation, morphology and clotrimazole sensitivity. Moreover, we determined the influence of growth phase and morphology per se on drug sensitivity. We showed that utilization of lactate as a carbon source did not promote fast fungal proliferation or filamentation. Lactate had no influence on clotrimazolemediated killing of C. albicans in standard fungal cultivation medium but had an additive effect on the fungicidal clotrimazole action under in vitro vagina-simulative conditions. Moreover, clotrimazole-mediated killing was growth-phase and morphology dependent. Post-exponential cells were resistant to the fungicidal action of clotrimazole, whilst logarithmic cells were sensitive, and hyphae showed the highest susceptibility. Finally, we showed that treatment of pre-formed C. albicans hyphae with sublethal concentrations of clotrimazole induced a reversion to yeast-phase growth. As C. albicans hyphae are considered the pathogenic morphology during mucosal infections, these data suggest that elevated fungicidal activity of clotrimazole against hyphae plus clotrimazole-induced hyphae-to-yeast reversion may help to dampen acute vaginal infections by reducing the relative proportion of hyphae and thus shifting to a non-invasive commensal-like population. In addition, lactate as an ingredient of clotrimazole formulations may potentiate clotrimazole killing of C. albicans in the vaginal microenvironment.

Candida albicans morphology: still in focus

“…This included filastatin [66], ascorbic acid [66], mucins [67], gymnemic acids [68], and quinacrine [69] to name only a few. Of note, even known antifungals seem to have specific effects on the different morphological forms of C. albicans, and one azole was shown to force the fungus into the yeast growth mode, potentially due to reduced ergosterol content of the cell membrane [70]. In agreement with that information, one study identified ergosterol synthesis as a critical aspect in a large-scale functional screening to identify regulators of morphogenesis [7].…”

Biofilm Formation of Candida albicans Facilitates Fungal Infiltration and Persister Cell Formation in Vaginal Candidiasis

“…Biofilm MIC 80 was determined as the lowest concentration that inhibited ≥80% of fungal biofilm growth. RPMI-1640 of pH 7.2 and pH 4.0 were used as growth medium, respectively, to examine the effect of different environmental acidity on antifungal efficacy as local pH has been found to impact on the antifungal-mediated killing of C. albicans (Ilkit and Guzel, 2011;Kasper et al, 2015).…”

Fonsecaea pedrosoi Sclerotic Cells: Secretion of Aspartic-Type Peptidase and Susceptibility to Peptidase Inhibitors

“…Moreover, antimicrobial activity can be microorganism- and/or morphology-dependent. Kasper et al (2015) compared the clotrimazole antifungal action against C. albicans morphotypes and showed that hyphae were much more sensitive to this azole than the yeast form. In fact, studies have showed that fungal morphological changes are usually associated with intense modification of cell surface, physiology and immunology ( Klein and Tebbets, 2007 ; Erwig and Gow, 2016 ).…”