Antifungal activity of Myriocin on clinically relevant Aspergillus fumigatus strains producing biofilm

Abstract

BackgroundThe human pathogenic mold Aspergillus fumigatus is able to form a complex biofilm embedded in extracellular matrix. Biofilms confer antimicrobial resistance and it is well known that aspergillosis is often refractory to the conventional antifungal therapy. The treatment of biofilm-related infections poses a significant clinical challenge on a daily basis, promoting the search for new therapeutic agents.Our aim was to exploit the modulation of sphingolipid mediators as new therapeutic target to overcome antifungal resistance in biofilm-related infections.ResultsAntifungal susceptibility testing was performed on 20 clinical isolates of Aspergillus fumigatus and one reference strain (A. fumigatus Af293) according the EUCAST protocol. Sessile MICs were assessed on 24-h preformed-biofilm by means of XTT-reduction assay. Myriocin (0.25–64 mg/L), a commercial sphingolipid synthesis inhibitor, was used. The MEC50 value (mg/L) of Myriocin was 8 (range 4–16) for both planktonic and sessile cells.Drug-induced morphological alterations were analyzed by optical and electron microscopy (TEM) on 24h preformed A. fumigatus Af293 biofilms.An evident hyphal damage, resulting in short, stubby, and highly branched hyphae was observed by optical microscopy. At 24h, TEM studies showed important morphological alterations, such as invaginations of the cell membrane, modification in the vacuolar system and presence of multilamellar bodies, in some cases within vacuoles.ConclusionsThe direct antifungal activity, observed on both planktonic and sessile fungi, suggests that inhibition of sphingolipid synthesis could represent a new target to fight biofilm-related A. fumigatus resistance.

Sphingolipids as Targets for Treatment of Fungal Infections

“…Although this step is conserved between mammalian and fungal sphingolipids biosynthesis, the use of myriocin has significantly contributed to understand the importance of sphingolipids in fungi [91]. Myriocin treatment against Candida and Aspergillus species impairs biofilm formation through inhibition of sphingolipid formation, leading to changes in lipid rafts distribution in fungal membranes and cell morphology [92,93]. Nevertheless, since …”

Antifungal constituents of the plant family Amaryllidaceae

“…Both compounds had MICs of 50 μg/ml against C. albicans , only Candidamide A ( 32 ) was active against A. niger (MIC 20 μg/ml), whereas out of the two, only Candidamide B ( 33 ) inhibited T. rubrum growth (MIC 40 μg/ml) (Wu et al, ). Precedence for the antifungal activities of ceramide compounds exists in the literature (Perdoni et al, ). For example, the commercial sphingolipid synthesis inhibitor Myriocin in Aspergillus fumigatus cultures exhibited a minimum effective concentration of 8 μg/ml (Perdoni et al, ).…”

Fungal Metabolites for the Control of Biofilm Infections

“…Myriocin acts by strong inhibition of serine palmitoyltransferase, a key enzyme in the synthesis of sphingolipids [73]. It has been demonstrated that C. albicans biofilms possess a higher ratio of sphingolipids than planktonic cells, and accordingly, treatment with myriocin completely prevented the formation of C. albicans biofilms [74], as well as biofilms of Aspergillus fumigatus clinical isolates [75]. Although these reports are rather optimistic, one should keep in mind that myriocin is toxic for eukaryotes and has a small therapeutic window.…”