In vitro synergism of a water insoluble fraction of Uncaria tomentosa combined with fluconazole and terbinafine against resistant non-Candida albicans isolates

Caryocar coriaceum fruits as a potential alternative to combat fungal and bacterial infections: In vitro evaluation of methanolic extracts

Caryocar coriaceum, commonly known as 'pequi', is a medicinal species used traditionally for the herbal treatment of infectious and parasitic diseases in the Brazilian Northeast region. In this study, we investigated whether the fruits of C. coriaceum have bioactive chemical constituents against etiological agents of infectious diseases. The methanolic extract of the internal mesocarp of the fruits of C. coriaceum (MECC) was chemically analyzed and evaluated for its antimicrobial and drug-enhancing activity against multidrug-resistant pathogenic bacteria (Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus), and Candida spp. strains. The extract had flavones, flavonols, xanthones, catechins, and flavanones as major classes. A total of 11.26 mg GAE/g of phenolics, and 5.98 mg QE/g of flavonoids were found. No intrinsic antibacterial activity was observed; however, the extract was able to intensify the action of gentamicin and erythromycin against multi-resistant strains. The anti-Candida effect observed in this study was mainly due to the formation of reactive oxygen species. The extract was capable of causing damage to the plasmatic membrane of Candida tropicalis through pores formation. Our findings partially support the ethnopharmacological uses of the fruit pulp of C. coriaceum against infectious and parasitic diseases.

Antifungal Activity of Plant Secondary Metabolites on Candida albicans: An Updated Review

Fungal infections have been increasing continuously worldwide, especially in immunocompromised individuals. Fungi, regarded as eukaryotic pathogens, have many similarities to the host cells, which inhibit anti-fungal drug development progress. Various fungal model systems have been studied, and it was concluded that Candida spp. is the most common disease-causing fungus. Candida species are well known to cause infections not only in our mouth, skin, and vagina, but they are also a frequent cause of life-threatening hospital bloodstream infections. The morphological and developmental pathways of Candida have been studied extensively, providing insight into the fungus development. Candida albicans is known to be the most pathogenic species responsible for a variety of infections in humans. Conventional anti-fungal drugs, mainly azoles drugs available in the market, have been used for years developing resistance in C. albicans. Hence, the production of new anti-fungal drugs, which require detailed molecular knowledge of fungal pathogenesis, needs to be encouraged. Therefore, this review targets the new approach of "Green Medicines" or the phytochemicals and their secondary metabolites as a source of novel anti-fungal agents to overcome the drug resistance of C. albicans, their mechanism of action, and their combined effects with the available anti-fungal drugs.

Augmenting Azoles with Drug Synergy to Expand the Antifungal Toolbox

Fungal infections impact the lives of at least 12 million people every year, killing over 1.5 million. Wide-spread use of fungicides and prophylactic antifungal therapy have driven resistance in many serious fungal pathogens, and there is an urgent need to expand the current antifungal arsenal. Recent research has focused on improving azoles, our most successful class of antifungals, by looking for synergistic interactions with secondary compounds. Synergists can co-operate with azoles by targeting steps in related pathways, or they may act on mechanisms related to resistance such as active efflux or on totally disparate pathways or processes. A variety of sources of potential synergists have been explored, including pre-existing antimicrobials, pharmaceuticals approved for other uses, bioactive natural compounds and phytochemicals, and novel synthetic compounds. Synergy can successfully widen the antifungal spectrum, decrease inhibitory dosages, reduce toxicity, and prevent the development of resistance. This review highlights the diversity of mechanisms that have been exploited for the purposes of azole synergy and demonstrates that synergy remains a promising approach for meeting the urgent need for novel antifungal strategies.

Update on Candida krusei, a potential multidrug-resistant pathogen

Although Candida albicans remains the main cause of candidiasis, in recent years a significant number of infections has been attributed to non-albicans Candida (NAC) species, including Candida krusei. This epidemiological change can be partly explained by the increased resistance of NAC species to antifungal drugs. C. krusei is a diploid, dimorphic ascomycetous yeast that inhabits the mucosal membrane of healthy individuals. However, this yeast can cause life-threatening infections in immunocompromised patients, with hematologic malignancy patients and those using prolonged azole prophylaxis being at higher risk. Fungal infections are usually treated with five major classes of antifungal agents which include azoles, echinocandins, polyenes, allylamines, and nucleoside analogues. Fluconazole, an azole, is the most commonly used antifungal drug due to its low host toxicity, high water solubility, and high bioavailability. However, C. krusei possesses intrinsic resistance to this drug while also rapidly developing acquired resistance to other antifungal drugs. The mechanisms of antifungal resistance of this yeast involve the alteration and overexpression of drug target, reduction in intracellular drug concentration and development of a bypass pathway. Antifungal resistance menace coupled with the paucity of the antifungal arsenal as well as challenges involved in antifungal drug development, partly due to the eukaryotic nature of both fungi and humans, have left researchers to exploit alternative therapies. Here we briefly review our current knowledge of the biology, pathophysiology and epidemiology of a potential multidrug-resistant fungal pathogen, C. krusei, while also discussing the mechanisms of drug resistance of Candida species and alternative therapeutic approaches.

Current Aspects in the Biology, Pathogeny, and Treatment of Candida krusei, a Neglected Fungal Pathogen

Fungal infections represent a constant and growing menace to human health, because of the emergence of new species as causative agents of diseases and the increment of antifungal drug resistance. Candidiasis is one of the most common fungal infections in humans and is associated with a high mortality rate when the fungi infect deep-seated organs. Candida krusei belongs to the group of candidiasis etiological agents, and although it is not isolated as frequently as other Candida species, the infections caused by this organism are of special relevance in the clinical setting because of its intrinsic resistance to fluconazole. Here, we offer a thorough revision of the current literature dealing with this organism and the caused disease, focusing on its biological aspects, the host-fungus interaction, the diagnosis, and the infection treatment. Of particular relevance, we provide the most recent genomic information, including the gene prediction of some putative virulence factors, like proteases, adhesins, regulators of biofilm formation and dimorphism. Moreover, C. krusei veterinary aspects and the exploration of natural products with anti-C. krusei activity are also included.

Anti-Fungal Efficacy and Mechanisms of Flavonoids

The prevalence of fungal infections is growing at an alarming pace and the pathogenesis is still not clearly understood. Recurrence of these fungal diseases is often due to their evolutionary avoidance of antifungal resistance. The development of suitable novel antimicrobial agents for fungal diseases continues to be a major problem in the current clinical field. Hence, it is urgently necessary to develop surrogate agents that are more effective than conventional available drugs. Among the remarkable innovations from earlier investigations on natural-drugs, flavonoids are a group of plant-derived substances capable of promoting many valuable effects on humans. The identification of flavonoids with possible antifungal effects at small concentrations or in synergistic combinations could help to overcome this problem. A combination of flavonoids with available drugs is an excellent approach to reduce the side effects and toxicity. This review focuses on various naturally occurring flavonoids and their antifungal activities, modes of action, and synergetic use in combination with conventional drugs.

Promising antifungal activity of new oxadiazole against Candida krusei

Candida krusei is one of the most common agents of invasive candidiasis and candidemia worldwide, leading to high morbidity and mortality rates. This species has become a problem due to its intrinsic resistance and reduced susceptibility to azoles and polyenes. Moreover, the number of antifungal drugs available for candidiasis treatment is limited, demonstrating the urgent need for the discovery of novel alternative therapies. In this work, the in vivo and in vitro activities of a new oxadiazole (LMM11) were evaluated against C. krusei. The minimum inhibitory concentration ranged from 32 to 64 μg/mL with a significant reduction in the colony forming unit (CFU) count (~3 log₁₀). LMM11 showed fungicidal effect, similar to amphotericin, reducing the viable cell number (>99.9%) in the time-kill curve. Yeast cells presented morphological alterations and inactive metabolism when treated with LMM11. This compound was also effective in decreasing C. krusei replication inside and outside macrophages. A synergistic effect between fluconazole and LMM11 was observed. In vivo treatment with the new oxadiazole led to a significant reduction in CFU (0.85 log₁₀). Furthermore, histopathological analysis of the treated group exhibited a reduction in the inflammatory area. Taken together, these results indicate that LMM11 is a promising candidate for the development of a new antifungal agent for the treatment of infections caused by resistant Candida species such as C. krusei.

Antifungals discovery: an insight into new strategies to combat antifungal resistance

Undeniably, new antifungal treatments are necessary against pathogenic fungi. Fungal infections have significantly increased in recent decades, being highlighted as important causes of morbidity and mortality, particularly in immunocompromised patients. Five main antifungal classes are used: (i) azoles, (ii) echinocandins, (iii) polyenes, (iv) allylamines and (v) pyrimidine analogues. Moreover, the treatment of mycoses has several limitations, such as undesirable side effects, narrow activity spectrum, a small number of targets and fungal resistance, which are still of major concern in clinical practice. The discovery of new antifungals is mostly achieved by the screening of natural or synthetic/semisynthetic chemical compounds. The most recent discoveries in drug resistance mechanism and their avoidance were explored in a review, focusing on different antifungal targets, as well as new agents or strategies, such as combination therapy, that could improve antifungal therapy.

SIGNIFICANCE AND IMPACT OF THE STUDY

The failure to respond to antifungal therapy is complex and is associated with microbiological resistance and increased expression of virulence in fungal pathogens. Thus, this review offers an overview of current challenges in the treatment of fungal infections associated with increased antifungal drug resistance and the formation of biofilms in these opportunistic pathogens. Furthermore, the most recent and potential strategies to combat fungal pathogens are explored here, focusing on new agents as well as innovative approaches, such as combination therapy between antifungal drugs or with natural compounds.