<i>In Vitro</i> Efficacy of Continuous Mild Heat Stress on the Antifungal Susceptibility of <i>Candida albicans</i> Biofilm Formation

Abstract

Elevation in the temperature induces heat stress to both host cells and the invading pathogen. This study aimed to determine whether continuous mild heat stress (increased temperature without causing significant damage to host cells) can increase susceptibility of biofilm formation of the opportunistic fungal pathogen Candida albicans to low concentrations of three typical antifungal agents. In this way the side effects associated with higher concentrations of the antifungal agents on host cells would be reduced. Fluconazole and micafungin at concentrations ranging from 0.0625 to 2 µg/mL and amphotericin B at concentrations ranging from 0.0625 to 1 µg/mL inhibited less than 20% of cells in biofilm formation. Biofilm formation at 39 or 41°C compared to 37°C resulted in increased susceptibility to the three agents, but especially micafungin. These data suggest that mild heat stress (39°C) would be valuable for increasing the effectiveness of low concentrations of antifungal agents against C. albicans biofilm formation. Thus, the concept of continuous mild heat stress at the site of insertion of medical devices or catheters combined with antifungal agents could be beneficial.Key words mild heat stress; antifungal susceptibility; biofilm formation; Candida albicans Candida albicans is a commensal of human mucosal surfaces and an opportunistic pathogen. C. albicans can form biofilms on medical implants and intravascular catheters resulting in biofilm-related infections and systemic candidiasis.1,2) Fungal biofilms are more resistant to antifungal agents, in particular azoles and polyenes, than planktonic cells. 3)β-1,3-Glucan levels of biofilm-associated C. albicans cell walls increased compared to planktonic cells and those of exogenous biofilm matrix was also elevated.4) Azoles and polyenes bind to the biofilm extracellular matrix including β-1,3-glucans and are prevented from getting to their targets. 4,5) Echinocandins are better than azoles and polyenes for treating biofilms as they inhibit production of β-1,3-glucan. 6)Exogenous mild heat stress has been widely used as a physical therapy for treatment of muscle injury and malignant tumors. 7,8) On the other hand, endogenous mild heat stress (fever at around 39°C) that occurs during bacterial infections induced optimized cytokine expression and pathogen elimination.9) But fever at over 40°C would increase risk of collateral host injury in infected patients.10) Cowen and Lindquist 11) reported that high temperatures such as fever reduced resistance of planktonic cells of C. albicans clinical isolates to high concentrations of fluconazole in a defined medium. However, drug resistance of C. albicans in biofilm conditions is considered to occur through distinctly different mechanisms from the cells in planktonic conditions. 12)In this study, the effect of mild heat stress on the susceptibility of Candida albicans in biofilm formation to low concentrations of fluconazole, micafungin and amphotericin B was tested in vitro. MATERIALS AND METHODSC. albicans Strain C. al...

In Vitro Analyses of Mild Heat Stress in Combination with Antifungal Agents against Aspergillus fumigatus Biofilm

“…The germination times were much earlier and the germination rates higher at 39 and 41°C than those at the control temperature of 37°C. This result is similar to that described by Cho et al in their study of C. albicans biofilm formation (26). We also find that polar growth (i.e., coherent directional growth) was noticeable only at 37°C.…”

“…Cowen and Lindquist (25) found that the susceptibility of planktonic C. albicans cells from clinical isolates to fluconazole is increased by mild heat stress. Cho (26) believes that continuous mild heat stress increases the susceptibility of C. albicans biofilm to antifungal drugs, such as fluconazole, micafungin (MCF), and amphotericin B (AMB). Given the fact that A. fumigatus differs greatly from C. albicans with regard to genotype and phenotype, leading to its superior adaptability and more favorable entry, it is reasonable to determine whether antifungal drug susceptibilities are affected by mild heat stress in this pathogenic fungus.…”

Mild Heat Stress Affects on the Cell Wall Structure in <i>Candida albicans</i> Biofilm

“…This condition simulates fever symptoms in infectious diseases. In our previous report, mild heat stress induced the antifungal susceptibility of C. albicans SC5314 biofilm 9) . However, what occurred in the cells due to mild heat stress remained to be solved.…”

“…In particular, mild heat stress at two or four degrees higher than 37ºC led to increased susceptibility of C. albicans biofilm to antifungal agents such as micafungin, fluconazole, and amphotericin B. The difference in component ratio of yeast and hyphae at an early stage of biofilm formation may be the reason for the increased susceptibility of C. albicans biofilm to antifungal agents under conditions of mild heat stress, although the difference was observed only microscopically 9) . Moreover, biofilm at over 39ºC was observed to somewhat repress further biofilm growth.…”

“…Cowen and Lindquist have focused on fungal Hsp90 as a new therapeutic target based on a clinical benefit of fever 8) . We reported the effect of mild heat stress on the antifungal susceptibility of biofilm formation in C. albicans 9) . In particular, mild heat stress at two or four degrees higher than 37ºC led to increased susceptibility of C. albicans biofilm to antifungal agents such as micafungin, fluconazole, and amphotericin B.…”