Abstract
Aims: This study investigated the bioactivity of the crude leaf extract (CLE) and fractions hexane (HX) and ethyl acetate (EtOAc) from Talinum paniculatum alone and in association with fluconazole (FLC) against reference strain and clinical isolates of FLC-resistant Candida albicans. Furthermore, the antioxidant capability, chemical composition of this plant, and the effect’s underlying mechanisms were evaluated. Methods: The antifungal activity was evaluated using checkerboard assay to establish the minimum inhibitory (MIC) and minimum microbicidal concentrations (MMC). During FLC and plant products challenges, the reactive oxygen species (ROS) generation (hydroxyl radicals [HO•]) were detected in C. albicans cells using the membrane-permeable fluorescent probes APF and HPF. High-performance liquid chromatography (HPLC) profile, quantitative analysis of antioxidant compounds, and free radical scavenging activity (DPPH assay) tests were performed. Results: The CLE and fractions presented outstanding antifungal activity and selectivity against C. albicans cells but had no synergistic effects with FLC. The MIC values for CLE and its fractions against C. albicans reference strain were in the order of HX (31.25 μg ml–1) < EtOAc (62.5 μg ml–1) < CLE (500 μg ml–1), and against FLC-resistant C. albicans HX (125 μg ml–1) = EtOAc < CLE (500 μg ml–1). CLE and its fractions had more potent antifungal activities than FLC against the clinical isolates. Moreover, fungicidal effects for these plant products were demonstrated against FLC-resistant C. albicans, which further confirmed an antifungal potential. Conversely, during association, plant products were shown to cause an increase in FLC MIC anywhere from 2- to 16-fold. FLC exposure led to an increase in the steady-state levels of ROS (HO•) in C. albicans cells. Next, we found that the increases in FLC MICs were owing to action of antioxidants containing-CLE and its fractions in preventing FLC-induced ROS-mediated growth inhibition of C. albicans. Conclusion: T. paniculatum can be a source of bioactive compounds with antifungal potential. However, because of the common use of its edible leaf, caution is advised during therapy with FLC (since it can decrease FLC susceptibility).
Highlights
Over the last few decades, the relentless increase of antimicrobial resistance and multidrug resistance (AMR/MDR) in microorganisms has been observed in low, middle, and high-income countries and has resulted in mortality rates in patients who have hospital- or community-associated infections (HAI/CAI) reaching numbers comparable to the pre-antimicrobial era [1,2,3,4]
As observed in table 2, high minimum inhibitory concentration (MIC) values were observed with FLC measured against the isolates, in which both isolates of C. albicans were resistant to this antifungal agent (MIC ≥ 64 μg ml–1)
The MIC and minimum microbicidal concentrations (MMC) values for the crude leaf extract (CLE), EtOAc, HX, and FLC, measured against the reference strains of C. albicans and FLC-resistant C. albicans strains are presented in table 2
Summary
Over the last few decades, the relentless increase of antimicrobial resistance and multidrug resistance (AMR/MDR) in microorganisms has been observed in low-, middle-, and high-income countries and has resulted in mortality rates in patients who have hospital- or community-associated infections (HAI/CAI) reaching numbers comparable to the pre-antimicrobial era [1,2,3,4]. The spread of resistance, emergence of highly virulent and pathogenic strains of C. albicans that commensally colonize 30-70% of healthy individuals, and formation of biofilms underlie chronic and recurrent infections have increased the ability of this microorganism to cause disease, further aggravating the issue of AMR/MDR. These factors are, at least partially, responsible for the high invasive fungal infections (IFIs) and mortality rates from C. albicans infections [2]. In Brazil, the real data are still underestimated, but studies have showed a considerable prevalence of Fluconazole-resistant C. albicans infections, and besides the natural process of AMR/ MDR, the inadequate antimicrobial use (most from food production) is the single most important factor leading to antibiotic resistance in this country [9,10,11,12]
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