In vitro analyses of mild heat stress in combination with antifungal agents against Aspergillus fumigatus biofilm

Utilizing the photodynamic properties of curcumin to disrupt biofilms in Cutibacterium acnes: A promising approach for treating acne

BACKGROUND

The treatment of acne vulgaris is often challenging due to the antibiotic resistance frequently observed in Cutibacterium acnes (C.acnes), a prevalent bacterium linked to this condition.

OBJECTIVE

The objective of this research was to examine the impact of curcumin photodynamic therapy (PDT) on the survival of C.acnes and activity of biofilms produced by this microorganism.

METHODS

Following the Clinical and Laboratory Standards Institute (CLSI) guidelines, we assessed the drug sensitivity of 25 clinical C.acnes strains to five antibiotics (erythromycin, clindamycin, tetracycline, doxycycline, minocycline) and curcumin by implementing the broth microdilution technique. In addition, we established C.acnes biofilms in a laboratory setting and subjected them to curcumin-PDT(curcumin combined with blue light of 180 J/cm2). Afterwards, we evaluated their viability using the XTT assay and observed them using confocal laser scanning microscopy.

RESULTS

The result revealed varying resistance rates among the tested antibiotics and curcumin, with erythromycin, clindamycin, tetracycline, doxycycline, minocycline, and curcumin exhibiting resistance rates of 72 %, 44 %, 36 %, 28 %, 0 %, and 100 %, respectively. In the curcumin-PDT inhibition tests against four representative antibiotic-resistant strains, it was found that the survival rate of all strains of planktonic C. acnes was reduced, and the higher the concentration of curcumin, the lower the survival rate. Furthermore, in the biofilm inhibition tests, the vitality and three-dimensional structure of the biofilms were disrupted, and the inhibitory effect became more significant with higher concentrations of curcumin.

CONCLUSION

The results emphasize the possibility of using curcumin PDT as an alternative approach for the treatment of C.acnes, especially in instances of antibiotic-resistant variations and infections related to biofilms.

Effect of 5-Aminolevulinic Acid Photodynamic Therapy on Aspergillus fumigatus Biofilms in Vitro

Aspergillus fumigatus biofilm development results in enhanced pathogenicity and treatment resistance. Most contemporary antibiotics, however, are unable to eliminate biofilms. In recent years, with the application of new photosensitizers and the development of treatment, ALA-PDT (5-aminolevulinic acid photodynamic treatment) has achieved remarkable curative effect in the treatment of fungal infectious diseases; however, no research has been conducted on ALA-PDT against A. fumigatus. This study investigated the inhibitory effect of ALA-PDT at various 5-aminolevulinic acid concentrations and light doses on A. fumigatus planktonic and biofilms in vitro. We found that ALA-PDT may successfully inhibit the development of A. fumigatus biofilm and disintegrate mature biofilm. After ALA-PDT treatment, the adherence rate and vitality dramatically decreased, and the biofilm's structure was severely compromised. Our findings show for the first time that ALA-PDT may be used to prevent the formation of A. fumigatus biofilm and disturb the structure of mature biofilm, and that it could be employed as a therapeutic therapy for A. fumigatus superficial infection.

Interaction of Amiodarone with Azoles Against Aspergillus Planktonic Cells and Biofilms in vitro

Aspergillus spp. is the most common clinical pathogen of invasive fungal infection with high mortality. Existing treatments for Aspergillus spp. infection are still inefficient and accompanied by drug resistance, so it is still urgent to find new treatment approaches. The antiarrhythmic drug amiodarone (AMD) has demonstrated antifungal activity against a range of fungi. This study evaluated the efficacy of AMD in combination with triazoles for Aspergillus spp. infection. We tested the combined effect of AMD and three triazole drugs, namely, itraconazole (ITR), voriconazole (VRC), and posaconazole (POS), on the planktonic cells and biofilms of 20 strains of Aspergillus spp. via a checkerboard microdilution assay derived from 96-well plate-based method. Our results reveal that the combination of AMD with ITR or POS against Aspergillus biofilms has synergistic fungicidal effects. By contrast, the combination of AMD with VRC exhibits no antagonistic and synergistic effects. In this way, the use of AMD in combination with ITR or POS could be an effective adjunctive treatment for Aspergillus spp. infection.

Effects of Itraconazole and Micafungin on Aspergillus fumigatus Biofilms

Aspergillus fumigatus (A. fumigatus) is the most common airborne opportunistic fungal pathogen. Biofilm formation is one of the main pathogenic mechanisms of A. fumigatus. During the past decades, A. fumigatus azole resistance has become prevalent due to the medical and agricultural use of antifungal drugs and fungicides. Until now, the role of fungal biofilms in azole resistance of A. fumigatus remains unclear. In the present study, we compared biofilm drug susceptibility and biofilm formation under itraconazole of azole-resistant strains, sensitive strains, and standard strains, separately. The biofilm viability and matrix thickness at the early and the late stage were measured by XTT assay and Calcofluor white. Our results showed that the sessile minimum inhibitory concentration of itraconazole, which describing the inhibition of drugs on fungi sessile with biofilm, was much higher than the traditional minimal inhibitory concentration of itraconazole. Additionally, low concentrations of itraconazole inhibited biofilm formation of A. fumigatus strains. Notably, biofilm formation by azole-resistant strains could not be inhibited by high concentrations of itraconazole but could be effectively restrained by low concentrations of micafungin, revealing the efficacy of a cell-wall inhibitor to disrupt A. fumigatus biofilm formation. However, late-stage biofilms of both azole-resistant strains and standard strains were hard to disrupt using itraconazole. We found that itraconazole was effective to prevent A. fumigatus biofilm formation at the early stage. For the treatment of A. fumigatus biofilm, our findings suggest that an early-stage preventive strategy is preferred and micafungin is effective to control the azole-resistant strain infection.

In Vitro Effects of Farnesol Alone and in Combination with Antifungal Drugs Against Aspergillus Clinical Isolates

Farnesol is an extracellular quorum-sensing molecule produced by Candida albicans. Farnesol is also a sesquiterpene alcohol existing in many herbal products and has various activity against fungal cells. We aimed to investigate the efficacy of farnesol alone and the contribution of farnesol on the activity of voriconazole and amphotericin B against Aspergillus clinical isolates in vitro. A total of 45 Aspergillus clinical isolates were used in this study. The MIC values of voriconazole, amphotericin B, and farnesol were determined using reference broth microdilution method. The interactions of farnesol with voriconazole and amphotericin B were investigated by the checkerboard method and evaluated based on the fractional inhibitor concentration index (FICI). The MIC ranges of farnesol, voriconazole, and amphotericin B were 1,500-6,000 μM, 0.125-1 μg/mL, and 0.125-0.5 μg/mL against Aspergillus fumigatus isolates, 3,000-12,000 μM, 0.125-0.5 μg/mL, and 0.25-2 μg/mL against Aspergillus flavus isolates, respectively. The most common interaction in combination tests was "no interaction," and synergistic interaction was not detected. The combinations of farnesol with voriconazole and amphotericin B had antagonistic activity against 38% and 27% of all isolates, respectively.We concluded that the responses of different fungal species against farnesol are variable, and different interactions may be observed when it is combined with different antifungals. Therefore, it should be noted that farnesol may have an adverse effect on some fungi or interact negatively with antifungals used in combination.

Mild Heat Stress Affects on the Cell Wall Structure in Candida albicans Biofilm

We previously reported that Candida albicans responded to mild heat stress in a range of temperature elevations simulating fever, and concluded that mild heat stress increases susceptibility to antifungal drugs. In this study, we show that mild heat stress causes a morphological change in hyphae during the process of biofilm formation. We found that mild heat stress extended the period of hyphal stage maintenance in C. albicans biofilm. Although the rate of hyphal change from yeast form to hyphal form reached the maximum within 3 hr, later, almost every cell quickly reverted to the yeast growth phase within 6 hr at 37°C but not at 39°C, or under mild heat stress. Electron microscopy using a smart specimen preparation technique revealed that mild heat stress significantly increased the thickness of the inner cell wall accompanied by a decrease in density of the outer cell wall in the hyphae of C. albicans biofilm. To identify the gene responsible for the morphological changes associated with mild heat stress, we performed microarray gene expression analysis. Eleven genes were upregulated and 17 genes were downregulated under mild heat stress in biofilm cells. The increased PHR1 gene expression in response to mild heat stress was confirmed in quantitative RT-PCR analysis. The mutant upregulated PHR1 expression showed the same sensitivity against antifungal drug micafungin as dependent on mild heat stress. Our findings point to possible therapeutic effects of hyperthermia as well as to the effect of fever during infections.

The fungal cell wall as a target for the development of new antifungal therapies

In the past three decades invasive mycoses have globally emerged as a persistent source of healthcare-associated infections. The cell wall surrounding the fungal cell opposes the turgor pressure that otherwise could produce cell lysis. Thus, the cell wall is essential for maintaining fungal cell shape and integrity. Given that this structure is absent in host mammalian cells, it stands as an important target when developing selective compounds for the treatment of fungal infections. Consequently, treatment with echinocandins, a family of antifungal agents that specifically inhibits the biosynthesis of cell wall (1-3)β-D-glucan, has been established as an alternative and effective antifungal therapy. However, the existence of many pathogenic fungi resistant to single or multiple antifungal families, together with the limited arsenal of available antifungal compounds, critically affects the effectiveness of treatments against these life-threatening infections. Thus, new antifungal therapies are required. Here we review the fungal cell wall and its relevance in biotechnology as a target for the development of new antifungal compounds, disclosing the most promising cell wall inhibitors that are currently in experimental or clinical development for the treatment of some invasive mycoses.

Heat Stress Modulates Mycelium Growth, Heat Shock Protein Expression, Ganoderic Acid Biosynthesis, and Hyphal Branching of Ganoderma lucidum via Cytosolic Ca2

Heat stress (HS) influences the growth and development of organisms. Thus, a comprehensive understanding of how organisms sense HS and respond to it is required. Ganoderma lucidum, a higher basidiomycete with bioactive secondary metabolites, has become a potential model system due to the complete sequencing of its genome, transgenic systems, and reliable reverse genetic tools. In this study, we found that HS inhibited mycelium growth, reduced hyphal branching, and induced the accumulation of ganoderic acid biosynthesis and heat shock proteins (HSPs) in G. lucidum Our data showed that HS induced a significant increase in cytosolic Ca(2+) concentration. Further evidence showed that Ca(2+) might be a factor in the HS-mediated regulation of hyphal branching, ganoderic acid (GA) biosynthesis, and the accumulation of HSPs. Our results further showed that the calcium-permeable channel gene (cch)-silenced and phosphoinositide-specific phospholipase gene (plc)-silenced strains reduced the HS-induced increase in HSP expression compared with that observed for the wild type (WT). This study demonstrates that cytosolic Ca(2+) participates in heat shock signal transduction and regulates downstream events in filamentous fungi.

IMPORTANCE

Ganoderma lucidum, a higher basidiomycete with bioactive secondary metabolites, has become a potential model system for evaluating how environmental factors regulate the development and secondary metabolism of basidiomycetes. Heat stress (HS) is an important environmental challenge. In this study, we found that HS inhibited mycelium growth, reduced hyphal branching, and induced HSP expression and ganoderic acid biosynthesis in G. lucidum Further evidence showed that Ca(2+) might be a factor in the HS-mediated regulation of hyphal branching, GA biosynthesis, and the accumulation of HSPs. This study demonstrates that cytosolic Ca(2+) participates in heat shock signal transduction and regulates downstream events in filamentous fungi. Our research offers a new way to understand the mechanism underlying the physiological and metabolic responses to other environmental factors in G. lucidum This research may also provide the basis for heat shock signal transduction studies of other fungi.