Influence of heterocyclic and oxime-containing farnesol analogs on quorum sensing and pathogenicity in \u3ci\u3eCandida albicans\u3c/i\u3e

A series of synthetic molecules combining a geranyl backbone with a heterocyclic or oxime head group are quorum-sensing molecules that block the yeast to mycelium transition in the dimorphic fungus Candida albicans. A number of the analogs have an IC50 ≤ 10 μM, a level of potency essentially identical to the natural quorum sensing signal, the sesquiterpene farnesol. Two of the most potent analogs, neither toxic toward healthy mice, display remarkably different effects when co-administered with C. albicans. While neither offers protection from candidiasis, one analog mimics farnesol in acting as a virulence factor, whereas the other has no effect. The results offer the first example of highly potent synthetic fungal quorum-sensing molecules, and provide the first evidence for the ability to decouple quorum sensing and virulence

Enhanced pathogenicity of \u3ci\u3eCandida albicans \u3c/i\u3epre-treated with subinhibitory concentrations of fluconazole in a mouse model of disseminated candidiasis

Objectives: To investigate the relative pathogenicity of Candida albicans treated with subinhibitory concentrations of fluconazole in a mouse model of disseminated candidiasis. Previous studies indicate that these cells secrete 10 times more farnesol than do untreated cells. In our usage, subinhibitory means a concentration which causes a prominent decrease in turbidity but still allows some cell growth. Methods: C. albicans A72 cells were grown overnight in 0–5.0 mM fluconazole, washed, and inoculated in mice by tail vein injection. Groups of 15 or 16 mice were injected with 1.3 • 106cells and mortality was recorded for 7 days post-inoculation. The levels of farnesol in control and treated C. albicans were determined by GC/MS. Results: The MIC50 for strain A72 was 0.125 mg/L (0.4 mM). Mice administered C. albicans pre-treated with 0.5 to 1.0mMfluconazole died 2.5 to 4 days earlier and had 2 to 4 times higher mortality rates than mice given untreated C. albicans. Fluconazole (0.5 to 1.0 mM) pre-treated cells were 4.2 to 8.5 times more lethal (P \u3c 0.001)than untreated cells. The extracellular, membrane bound, and intracellular farnesol concentrations of cells pre-treated with 1.0 mM fluconazole were 12-, 2- and 6-times those of untreated cells. Conclusions: The effects of fluconazole on C. albicans are very concentration-dependent. The enhanced pathogenicity of fluconazole pre-treated C. albicans in mice should be relevant to the therapeutic and prophylactic use of fluconazole. Further research is needed to explore whether farnesol production by C. albicans is a virulence factor

Effect of Farnesol on a Mouse Model of Systemic Candidiasis, Determined by Use of a DPP3 Knockout Mutant of \u3ci\u3eCandida albicans\u3c/i\u3e

This work extends our previous observation that the fungus Candida albicans secretes micromolar levels of farnesol and that accumulation of farnesol in vitro prevents the yeast-to-mycelium conversion in a quorumsensing manner. What does farnesol do in vivo? The purpose of this study was to determine the role of farnesol during infection with a well-established mouse model of systemic candidiasis with C. albicans A72 administered by tail vein injection. This question was addressed by altering both endogenous and exogenous farnesol. For endogenous farnesol, we created a knockout mutation in DPP3, the gene encoding a phosphatase which converts farnesyl pyrophosphate to farnesol. This mutant (KWN2) produced six times less farnesol and was ca. 4.2 times less pathogenic than its SN152 parent. The strain with DPP3 reconstituted (KWN4) regained both its farnesol production levels and pathogenicity. These mutants (KWN1 to KWN4) retained their full dimorphic capability. With regard to exogenous farnesol, farnesol was administered either intraperitoneally (i.p.) or orally in the drinking water. Mice receiving C. albicans intravenously and farnesol (20 mM) orally had enhanced mortality (P \u3c 0.03). Similarly, mice (n = 40) injected with 1.0 ml of 20 mM farnesol i.p. had enhanced mortality (P \u3c 0.03), and the onset of mortality was 30 h sooner than for mice which received a control injection without farnesol. The effect of i.p. farnesol was more pronounced (P \u3c 0.04) when mice were inoculated with a sublethal dose of C. albicans. These mice started to die 4 days earlier, and the percent survival on day 6 postinoculation (p.i.) was five times lower than for mice receiving C. albicans with control i.p. injections. In all experiments, mice administered farnesol alone or Tween 80 alone remained normal throughout a 14-day observation period. Finally, beginning at 12 h p.i., higher numbers of C. albicans cells were detected in kidneys from mice receiving i.p. farnesol than in those from mice receiving control i.p. injections. Thus, reduced endogenous farnesol decreased virulence, while providing exogenous farnesol increased virulence. Taken together, these data suggest that farnesol may play a role in disease pathogenesis, either directly or indirectly, and thus may represent a newly identified virulence factor

In Vivo and In Vitro Anaerobic Mating in \u3ci\u3eCandida albicans\u3c/i\u3e

Candida albicans cells of opposite mating types are thought to conjugate during infection in mammalian hosts, but paradoxically, the mating-competent opaque state is not stable at mammalian body temperatures. We found that anaerobic conditions stabilize the opaque state at 37°C, block production of farnesol, and permit in vitro mating at 37°C at efficiencies of up to 84%. Aerobically, farnesol prevents mating because it kills the opaque cells necessary for mating, and as a corollary, farnesol production is turned off in opaque cells. These in vitro observations suggest that naturally anaerobic sites, such as the efficiently colonized gastrointestinal (GI) tract, could serve as niches for C. albicans mating. In a direct test of mating in the mouse GI tract, prototrophic cells were obtained from auxotrophic parent cells, confirming that mating will occur in this organ. These cells were true mating products because they were tetraploid, mononuclear, and prototrophic, and they contained the heterologous hisG marker from one of the parental strains