In Vitro Investigation of Antifungal Activity of Allicin Alone and in Combination with Azoles Against Candida Species

Activity of thonningianin A against Candida albicans in vitro and in vivo

Fungal infections are increasing rapidly, and antifungal agents used in clinics are limited. Therefore, novel antifungal agents with high efficiency are urgently required. In this study, we investigated the antifungal activity of thonningianin A (THA), a natural compound that is widely found in plants. We first determined the activity of THA against Candida albicans, one of the most common fungal pathogens, and found that THA showed antifungal activity against all C. albicans tested, including several fluconazole-resistant isolates. THA also inhibits the growth of non-Candida albicans species. In addition, THA displayed antibiofilm activity and could not only inhibit biofilm formation but also destroy mature biofilms. The in vivo antifungal efficacy of THA was confirmed in a Galleria mellonella infection model. Further studies revealed that THA could enhance intracellular reactive oxygen species (ROS) production and regulate the transcription of several redox-related genes. Specifically, caspase activity and expression of CaMCA1, a caspase-encoding gene in C. albicans, were remarkably increased upon THA treatment. Consistent with this, in the presence of THA, the Camca1 null mutant displayed higher survival rates and reduced caspase activity compared to the wild-type or CaMCA1-reintroduced strains, indicating an important role of CaMCA1 in the antifungal activity of THA. Taken together, our results indicate that THA possesses excellent antifungal activity and may be a promising novel antifungal candidate. KEY POINTS: • THA exhibits activity against Candida species, including fluconazole-resistant isolates • THA inhibits biofilm formation and destroys mature biofilm • Elevated ROS production and CaMCA1-mediated caspase activity are involved in the antifungal mechanisms of THA.

Photoactivated riboflavin inhibits planktonic and biofilm growth of Candida albicans and non-albicans Candida species

Fungal infections caused by Candida species pose a serious threat to humankind. Antibiotics abuse and the ability of Candida species to form biofilm have escalated the emergence of drug resistance in clinical settings and hence, rendered it more difficult to treat Candida-related diseases. Lethal effects of Candida infection are often due to inefficacy of antimicrobial treatments and failure of host immune response to clear infections. Previous studies have shown that a combination of riboflavin with UVA (riboflavin/UVA) light demonstrate candidacidal activity albeit its mechanism of actions remain elusive. Thus, this study sought to investigate antifungal and antibiofilm properties by combining riboflavin with UVA against Candida albicans and non-albicans Candida species. The MIC20 for the fluconazole and riboflavin/UVA against the Candida species tested was within the range of 0.125-2 μg/mL while the SMIC50 was 32 μg/mL. Present findings indicate that the inhibitory activities exerted by riboflavin/UVA towards planktonic cells are slightly less effective as compared to controls. However, the efficacy of the combination towards Candida species biofilms showed otherwise. Inhibitory effects exerted by riboflavin/UVA towards most of the tested Candida species biofilms points towards a variation in mode of action that could make it an ideal alternative therapeutic for biofilm-related infections.

Green synthesis of silver nanoparticles from discarded shells of velvet tamarind (Dialium cochinchinense) and their antimicrobial synergistic potentials and biofilm inhibition properties

In the field of nanomedicine, biogenic metal nanoparticles are commonly synthesized using edible plant products as bio-reducing or stabilizing agents. In this study, discarded shell of velvet tamarind fruit is explored as a potent reducing agent for biogenic synthesis of silver nanoparticles (VeV-AgNPs). Silver nanoparticles were formed in minutes under sunlight exposure, which was considerably fast compared to under ambient conditions. The optical, structural and morphological studies revealed that the nanoparticle colloidal solution consisted of particles with quasi-spherical and rodlike morphologies. To investigate antimicrobial properties, eight microorganisms were exposed to the VeV-AgNPs. The results indicated that VeV-AgNPs had enhanced antimicrobial activity, with a recorded minimum inhibitory concentration (MIC) of 3.9 µg/mL against E. coli. Further studies were conducted to examine the biofilm inhibition properties and synergistic effect of the VeV-AgNPs. The findings showed a biofilm inhibition potential of around 98% against E. coli, and the particles were also found to increase the efficacy of standard antimicrobial agents. The combinatory effect with standard antifungal and antibacterial agents ranged from synergistic to antagonistic effects against the tested microorganisms. These results suggest that silver nanoparticles produced from discarded shells of velvet tamarind are potent and could be used as a potential drug candidate to combat antimicrobial resistance.

Anticandidal Activity of In Situ Methionine γ-Lyase-Based Thiosulfinate Generation System vs. Synthetic Thiosulfinates

Candida albicans and non-albicans Candida species are a common cause of human mucosal infections, as well as bloodstream infections and deep mycoses. The emergence of resistance of Candida spp. to antifungal drugs used in practice requires the search for new antimycotics. The present study unravels the antifungal potential of the synthetic dialk(en)ylthiosulfinates in comparison with an enzymatic in situ methionine γ-lyase-based thiosulfinate generation system (TGS). The kinetics of the TGS reaction, namely, the methionine γ-lyase-catalyzed β-elimination of S-alk(en)yl-L-cysteine sulfoxides, was investigated via 1H NMR spectroscopy for the first time, revealing fast conversion rates and the efficient production of anticandidal dialk(en)ylthiosulfinates. The anticandidal potential of this system vs. synthetic thiosulfinates was investigated through an in vitro assay. TGS proved to be more effective (MIC range 0.36-1.1 μg/mL) than individual substances (MIC range 0.69-3.31 μg/mL). The tested preparations had an additive effect with the commercial antimycotics fluconazole, amphotericin B and 5-flucytosine demonstrating a fractional inhibitory coefficient index in the range of 0.5-2 μg/mL. TGS can be regarded as an attractive candidate for the targeted delivery of antimycotic thiosulfinates and for further implementation onto medically implanted devices.

Hyphae-specific genes: Possible molecular targets for magnetic iron oxide nanoparticles alone and combined with visible light in Candida albicans

Candida albicans readily develops resistance to fluconazole. Magnetic iron oxide nanoparticles (denoted as MION) and antimicrobial photodynamic therapy are attracting attention as therapeutic agents. This study aims to investigate the inhibitory efficacy of MION alone and combined with visible light against C. albicans and expression analysis of hyphal wall protein 1 (HWP1) and agglutinin-like sequence 1 (ALS1) genes in C. albicans. Antifungal susceptibility testing, photodynamic activity assay, reactive oxygen species (ROS) production assay and gene expression analysis were determined in C. albicans treated with MION alone and combined with visible light. MION at 1 × minimum inhibitory concentration (MIC) level (500 μg/mL) exhibited antifungal activity against C. albicans isolates. Further, 1 × MIC levels of MION alone and combined with visible light displayed remarkable fungicidal effects at 24 and 48 h after treatment. The MION combined with visible light caused the highest levels of ROS production by all C. albicans isolates. The relative RT-PCR data showed significant downregulation of HWP1 and ALS1 genes which are the key virulence genes in C. albicans. Differences in gene expression of  HWP1 and ALS1 were more significant in MION combined with visible light treatments than MION alone. Our study sheds a novel light on facile development of effective treatment of C. albicans especially fluconazole-resistant C. albicans infections. The hyphae-specific genes HWP1 and ALS1 could be probable molecular targets for MION alone and combined with visible light in C. albicans.

Isolation and Identification of Flavanone Derivative Eriodictyol from the Methanol Extract of Afzelia africana Bark and Its Antimicrobial and Antioxidant Activities

Background

Afzelia africana is a plant species with well-documented ethnobotanical and medicinal properties. The plant is reported to have various secondary metabolites and had been applied for the treatment of various diseased conditions.

Objectives

The study objectives include fractionation, isolation, purification, and characterization of eriodictyol from the bark of A. africana, and the determination of its antimicrobial and antioxidant activities. Methodology. The series of methodologies that were employed include fractionations and purification (column chromatography), characterization (HPLC, LC-MS, IR, ¹H, ¹³C, DEPT-135, HSQC, and HMBC), antimicrobial assays (microbroth dilution and checkerboard assay), and antioxidant activities assays (ABTS and DPPH scavenging capacity).

Results

The study reports the identification and characterization of eriodictyol from the bark of A. africana which exhibited potent antioxidant activities against ABTS and DPPH radicals with scavenging capacities (SC₅₀) of 2.14 ± 0.05 and 2.51 ± 0.06 µg/mL, respectively. The compound exhibited its antimicrobial activity by reporting good bacteriostatic activities (MBC/MIC > 4) against Staphylococcus aureus (SA), methicillin-resistant Staphylococcus aureus (MRSA), and fluconazole-resistant Candida albicans (CA2). Moreover, a broad spectrum of bactericidal effects (MBC/MIC ≤ 4) was reported against Streptococcus mutans (SM), Escherichia coli (EC), Bacillus subtilis (BS), Klebsiella pneumonia (KP), Pseudomonas aeruginosa (PA), Salmonella typhi (ST), and standard Candida albicans (CA1). The compound further exhibited synergistic effects against EC, KP, ST, and MRSA; ST; and CA2 when combined with ciprofloxacin, tetracycline, and nystatin, respectively. However, antagonistic effects were observed against PA and CA1 when combined with ciprofloxacin and ketoconazole, respectively.

Conclusion

The study reports for the first time the identification of eriodictyol from the bark of A. africana which exhibited significant antioxidant and antimicrobial properties.

Green synthesis of silver nanoparticles from peel extract of Chrysophyllum albidum fruit and their antimicrobial synergistic potentials and biofilm inhibition properties

Current methods for green synthesis of metal nanoparticles often require continuous harvesting of fresh bio-materials for every synthesis cycle. Practices and procedures that economize bio-materials need to be employed if green synthesis could become a sustainable and eco-friendly method for synthesizing metal nanoparticles. This study explores Chrysophyllum albidum peels (mostly regarded as waste) to prepare silver nanoparticles (Alb-AgNPs). The technique employed in the synthesis allows repeated use of the peels, thus, reducing the heavy dependence on bio-materials. The optical and structural properties of the Alb-AgNPs were studied with Scanning electron microscope, Fourier transform infrared spectrometer, UV-Vis spectrophotometer and powder X-ray diffractometer. The antimicrobial properties of the Alb-AgNPs were studied with selected microorganisms namely; S. aureus, E. coli, K. pneumoniae, B. subtilis, S. mutans, P. aeruginosa, S. typhi, and Candida albicans. High inhibitory activity against the microorganisms were exhibited with MICs ranging from 15.62 to 1000 µg/mL. Again, the Alb-AgNPs showed the ability to enhance the efficacy of standard antimicrobial agents. The results of the combined interaction with standard antibacterial and antifungal agents ranged from synergistic to antagonistic effects against the tested microorganisms. In addition, the Alb-AgNPs could serve as a biofilm inhibitor with the highest percent inhibition of about 92% against methicillin-resistant Staphylococcus aureus. The results from this study thus provide access to the simple, sustainable, economic and eco-friendly synthesis of silver nanoparticles with efficient antimicrobial properties as drug candidates as a means of overcoming the prevailing antibiotic resistance menaces.

An Assessment of the In Vitro Models and Clinical Trials Related to the Antimicrobial Activities of Phytochemicals

An increased number antibiotic-resistant bacteria have emerged with the rise in antibiotic use worldwide. As such, there has been a growing interest in investigating novel antibiotics against antibiotic-resistant bacteria. Due to the extensive history of using plants for medicinal purposes, scientists and medical professionals have turned to plants as potential alternatives to common antibiotic treatments. Unlike other antibiotics in use, plant-based antibiotics have the innate ability to eliminate a broad spectrum of microorganisms through phytochemical defenses, including compounds such as alkaloids, organosulfur compounds, phenols, coumarins, and terpenes. In recent years, these antimicrobial compounds have been refined through extraction methods and tested against antibiotic-resistant strains of Gram-negative and Gram-positive bacteria. The results of the experiments demonstrated that plant extracts successfully inhibited bacteria independently or in combination with other antimicrobial products. In this review, we examine the use of plant-based antibiotics for their utilization against antibiotic-resistant bacterial infections. In addition, we examine recent clinical trials utilizing phytochemicals for the treatment of several microbial infections.

Synergistic Effect of the Combination of Deferoxamine and Fluconazole In Vitro and In Vivo against Fluconazole-Resistant Candida Spp

The opportunistic fungal infections are an increasing threat to humans due to the increasing number of patients with immunodeficiency, in which the most popular fungal pathogen is Candida albicans . Fluconazole (FLC) is the common drug for treating C. albicans infections, but increasing drug resistance has limited its clinical use.

Antibiofilm Activity of Azadirachta indica and Catharanthus roseus and Their Synergistic Effects in Combination with Antimicrobial Agents against Fluconazole-Resistant Candida albicans Strains and MRSA

The rapid emergence and spread of antimicrobial resistance has become a global public health concern that threatens the effective treatment of infectious diseases. One major approach adopted to overcome antimicrobial resistance is the use of plant extracts individually and/or with combination of antibiotics with plant extracts, which may lead to new ways of treating infectious diseases and essentially representing a potential area for further future investigations. In this study, the antifungal activities of Azadirachta indica leaf and Catharanthus roseus flower extracts against fluconazole-resistant Candida albicans strains (isolated from pregnant women with vulvovaginal candidiasis) and anti-methicillin-resistant Staphylococcus aureus (MRSA) were evaluated by agar well diffusion, microdilution, and biofilm inhibition assays. Subsequently, the determination of the combined antimicrobial activity of the individual plant extracts with (fluconazole and voriconazole) and (ampicillin, tetracycline, and streptomycin) against C. albicans strains and MRSA, respectively, was evaluated by checkerboard microdilution assay. Results from the study showed that the antimicrobial activity of the two plant extracts determined by time-kill kinetics was fungistatic with their MICs ranging from 0.1 to 4 mg/mL. Interestingly, all extracts were proved as good biofilm inhibitors of resistant C. albicans and MRSA from 10.1 to 98.82%. Their combination interaction with fluconazole, voriconazole, ampicillin, tetracycline, and streptomycin ranged from synergy to antagonism as per the parameters used. Overall, these results showed that A. indica leaf and C. roseus flower extracts have significant antifungal property. Furthermore, A. indica leaf and C. roseus flower extracts alone or in combination with fluconazole and voriconazole could provide a promising approach to the management of candidiasis caused by drug-resistant strains as well as their interaction with the antibacterial agents to combat the common infections caused by MRSA.

Antifungal Activity and Potential Mechanism of 6,7, 4'-O-Triacetylscutellarein Combined With Fluconazole Against Drug-Resistant C. albicans

The increased resistance of Candida albicans to conventional antifungal drugs poses a huge challenge to the clinical treatment of this infection. In recent years, combination therapy, a potential treatment method to overcome C. albicans resistance, has gained traction. This study assessed the effect of 6,7,4′-O-triacetylscutellarein (TA) combined with fluconazole (FLC) on C. albicans in vitro and in vivo. TA combined with FLC showed good synergistic antifungal activity against drug-resistant C. albicans in vitro, with a partial inhibitory concentration index (FICI) of 0.0188–0.1800. In addition, the time-kill curve confirmed the synergistic effect of TA and FLC. TA combined with FLC showed a strong synergistic inhibitory effect on the biofilm formation of resistant C. albicans. The combined antifungal efficacy of TA and FLC was evaluated in vivo in a mouse systemic fungal infection model. TA combined with FLC prolonged the survival rate of mice infected with drug-resistant C. albicans and reduced tissue invasion. TA combined with FLC also significantly inhibited the yeast-hypha conversion of C. albicans and significantly reduced the expression of RAS-cAMP-PKA signaling pathway-related genes (RAS1 and EFG1) and hyphal-related genes (HWP1 and ECE1). Furthermore, the mycelium growth on TA combined with the FLC group recovered after adding exogenous db-cAMP. Collectively, these results show that TA combined with FLC inhibits the formation of hyphae and biofilms through the RAS-cAMP-PKA signaling pathway, resulting in reduced infectivity and resistance of C. albicans. Therefore, this study provides a basis for the treatment of drug-resistant C. albicans infections.

Synergistic potential of essential oils with antibiotics to combat fungal pathogens: Present status and future perspectives

The steady rise in the emergence of antibiotic-resistant fungal pathogens has rendered most of the clinical antibiotics available in the market to be ineffective. Therefore, alternative strategies are required to tackle drug-resistant fungal infections. An effective solution is to combine the available antibiotics with adjuvants such as phytochemicals or essential oils to enhance the efficacy and activity of antibiotics. The present review aims to summarize the studies on synergistic combinations of essential oils and anti-fungal antibiotics. The current findings, methods used for measuring synergistic effects, possible mechanisms of synergism, and future perspectives for developing synergistic EO-antibiotic therapeutic formulations are discussed in this study. Several essential oils exhibit synergistic effect in combination with antibiotics against human fungal pathogens such as Candida albicans. The possible mechanisms of synergy exhibited by essential oil- antibiotic combinations in fungi include disruption of cell wall structure/ ergosterol biosynthesis pathway, enhanced transdermal penetration of antibiotics, alterations in membrane permeability, intracellular leakage of cellular contents, inhibition of germ tube formation or fungal biofilm formation, and competition for a primary target. Synergistic combination of essential oils and antibiotics can prove to be a valid and pragmatic alternative to develop drugs with increased drug-efficacy, and low toxicity.

The Effects of Medicinal Plants and Bioactive Natural Compounds on Homocysteine

BACKGROUND

Among non-communicable diseases, cardiovascular diseases (CVDs) are the leading cause of mortality and morbidity in global communities. By 2030, CVD-related deaths are projected to reach a global rise of 25 million. Obesity, smoking, alcohol, hyperlipidemia, hypertension, and hyperhomocysteinemia are several known risk factors for CVDs. Elevated homocysteine is tightly related to CVDs through multiple mechanisms, including inflammation of the vascular endothelium. The strategies for appropriate management of CVDs are constantly evolving; medicinal plants have received remarkable attention in recent researches, since these natural products have promising effects on the prevention and treatment of various chronic diseases. The effects of nutraceuticals and herbal products on CVD/dyslipidemia have been previously studied. However, to our knowledge, the association between herbal bioactive compounds and homocysteine has not been reviewed in details. Thus, the main objective of this study is to review the efficacy of bioactive natural compounds on homocysteine levels according to clinical trials and animal studies.

RESULTS

Based on animal studies, black and green tea, cinnamon, resveratrol, curcumin, garlic extract, ginger, and soy significantly reduced the homocysteine levels. According to the clinical trials, curcumin and resveratrol showed favorable effects on serum homocysteine. In conclusion, this review highlighted the beneficial effects of medicinal plants as natural, inexpensive, and accessible agents on homocysteine levels based on animal studies. Nevertheless, the results of the clinical trials were not uniform, suggesting that more well-designed trials are warranted.

Antibacterial and Antifungal Activity of Propyl-Propane-Thiosulfinate and Propyl-Propane-Thiosulfonate, Two Organosulfur Compounds from Allium cepa: In Vitro Antimicrobial Effect via the Gas Phase

Propyl-propane thiosulfinate (PTS) and propyl-propane thiosulfonate (PTSO) are two volatile compounds derived from Allium cepa with a widely documented antimicrobial activity. The aim of this study was to evaluate their anti-candidiasis activity and the ability of its gaseous phase to inhibit bacterial and yeast growth in vitro. The minimum inhibitory concentration of various antifungal products (including PTS and PTSO) was determined versus 203 clinical isolates of Candida spp. through broth microdilution assay. Additionally, the antimicrobial activity through aerial diffusion of PTS and PTSO was evaluated over the growth of a collection of bacteria and yeasts cultivated in agar plates. All yeasts were susceptible to the antifungals tested, except C. glabrata and C. krusei, that showed azole resistance. PTSO (MIC₅₀ and MIC₉₀ ranged from 4 to 16 mg/L and 8 to 32 mg/L, respectively) was significantly more active against yeasts than PTS (MIC₅₀ and MIC₉₀ ranged from 16 to 64 mg/L and 32 to 64 mg/L). Values were higher than those obtained for antifungal drugs. Gaseous phases of PTS and PTSO generated growth inhibition zones whose diameters were directly related to the substances concentration and inversely related to the microbial inoculum. The quantification of PTS and PTSO levels reached in the growth media through aerial diffusion displayed a concentration gradient from the central zone to the periphery. Only P. aeruginosa ATCC 27853 showed resistance, while yeasts (C. albicans ATCC 200955 and C. krusei ATCC 6258) presented the higher susceptibility to both compounds. These results suggest that PTS and PTSO display antibacterial and anti-candidiasis activity in vitro through aerial diffusion, having potential use in human therapy.

Garlic alters the expression of putative virulence factor genes SIR2 and ECE1 in vulvovaginal C. albicans isolates

Vulvovaginal candidiasis causes sufferers much discomfort. Phytotherapy with garlic has been reported to be a possible alternative form of treatment; however, it is unknown why patients report varying success with this strategy. Fresh garlic extract has been shown to down-regulate the putative virulence gene, SIR2 in C. albicans. Our study aimed to see if previous observations were reproducible for the gene responsible for Candidalysin (ECE1). Two clinical strains from patients with reported variable efficacy of using garlic for the treatment of vulvovaginal candidiasis were compared through biofilm assays and antimicrobial susceptibility. Real-time PCR was used to assess changes in gene expression when exposed to garlic. Treatment with fresh garlic extract and pure allicin (an active compound produced in cut garlic) resulted in a decrease in SIR2 expression in all strains. In contrast, ECE1 expression was up-regulated in a reference strain and an isolate from a patient unresponsive to garlic therapy, while in an isolate from a patient responsive to garlic therapy, down-regulation of ECE1 occurred. Future studies that investigate the effectiveness of phytotherapies should take into account possible varying responses of individual strains and that gene expression may be amplified in the presence of serum.

The antimicrobial and antibiofilm properties of allicin against Candida albicans and Staphylococcus aureus - A therapeutic potential for denture stomatitis

The objective of this study is to determine the therapeutic efficacy of allicin against Candida albicans (C. albicans) and Staphylococcus aureus (S. aureus), the common etiological agents for denture stomatitis (DS). The minimum inhibitory concentration (MICs), minimum bactericidal concentrations (MBCs) and minimum fungicidal concentration (MFCs) of allicin were determined by the broth microdilution method followed by checkerboard microdilution method for a synergistic interaction between allicin + nystatin and allicin + CHX. The potential of allicin to eradicate C. albicans and S. aureus biofilms was assessed by treating biofilm formed on self- polymerized acrylic resin with allicin at a sub-MIC concentration for 5 min. The commercial denture cleanser (brand X) was used as a positive control. A Kruskal-Wallis test followed by the post-hoc Mann-Whitney U test was applied (SPSS 20.0), and the level of significance was set at P < 0.05. Allicin exhibited antimicrobial activity against C. albicans (MIC:8 µg/ml and MFC:16 µg/ml) and S. aureus (MIC:8 µg/ml and MBC:8 µg/ml). A synergistic interaction was observed between allicin + nystatin and allicin + CHX (FICI ≤ 0.5). Allicin exhibited significant biofilm eradication against C. albicans and S. aureus biofilms with percentages of 50.0% and 52.6%, respectively. The results of this study suggest a possible application of allicin in treating C. albicans and S. aureus infection in DS.

Exploration of Medicinal Plants as Sources of Novel Anticandidal Drugs

BACKGROUND

Human infections associated with skin and mucosal surfaces, mainly in tropical and sub-tropical parts of the world. During the last decade, there have been an increasing numbers of cases of fungal infections in immunocompromised patients, coupled with an increase in the number of incidences of drug resistance and toxicity to anti fungal agents. Hence, there is a dire need for safe, potent and affordable new antifungal drugs for the efficient management of candidal infections with minimum or no side effects.

INTRODUCTION

Candidiasis represents a critical problem to human health and a serious concern worldwide. Due to the development of drug resistance, there is a need for new antifungal agents. Therefore, we reviewed the different medicinal plants as sources of novel anticandidal drugs.

METHODS

The comprehensive and detailed literature on medicinal plants was carried out using different databases, such as Google Scholar, PubMed, and Science Direct and all the relevant information from the articles were analyzed and included.

RESULTS

Relevant Publications up to the end of November 2018, reporting anticandidal activity of medicinal plants has been included in the present review. In the present study, we have reviewed in the light of SAR and mechanisms of action of those plants whose extracts or phytomolecules are active against candida strains.

CONCLUSION

This article reviewed natural anticandidal drugs of plant origin and also summarized the potent antifungal bioactivity against fungal strains. Besides, mechanism of action of these potent active plant molecules was also explored for a comparative study. We concluded that the studied active plant molecules exhibit potential antifungal activity against resistant fungal strains.

Synergistic Interaction of Fluconazole/Amphotericin B on Inhibition of Enzymes Contributes to the Pathogenesis of Candida Tropicalis

Background: Candidiasis has gained much attention in recent decades due to its increasing prevalence in immunocompromised patients. Usually, antifungals such as fluconazole and amphotricin B are used for treatment of candidiasis, but one of the major clinical problems is the emergence of antifungal resistance. Combination antifungal therapy is one of the most commonly used methods to alleviate the problem of antifungal resistance. Methods: The effect of fluconazole alone and in combination with amphotericin B on C. tropicalis isolates were performed using the Clinical and Laboratory Standards Institute (CLSI) reference method. Eventually hypha formation, time kill study, proteinase and phospholipase activity and expression of PLB and SAP2 genes were carried out to investigate the enzymes inhibitory properties of antifungal tested against C. tropicalis. Results: Results showed the significant synergic effect of fluconazole in combination with amphotericin B in inhibiting the growth of C. tropicalis isolates, with fractional inhibitory concentration indices ranging from 0.06 to 0.5. The combination of fluconazole with amphotericin B reduced the number of yeast form and inhibited the yeast to hyphae transition in C. tropicalis. The antifungals tested were able to show the effect of down regulating expression of the selected genes significantly in fluconazole/amphotericin B ranging from 1.42- to 2.27-fold. Conclusion: Our results demonstrated that the synergistic interaction of fluconazole/amphotericin B would be worth exploring for the management of candidiasis. In addition, PLB and SAP2 genes could be probable molecular targets in the synergistic interaction of fluconazole/amphotericin B in C. tropicalis.

Eighty Years of Mycopathologia: A Retrospective Analysis of Progress Made in Understanding Human and Animal Fungal Pathogens

Mycopathologia was founded in 1938 to 'diffuse the understanding of fungal diseases in man and animals among mycologists.' This was an important mission considering that pathogenic fungi for humans and animals represent a tiny minority of the estimated 1.5-5 million fungal inhabitants on Earth. These pathogens have diverged from the usual saprotrophic lifestyles of most fungi to colonize and infect humans and animals. Medical and veterinary mycology is the subdiscipline of microbiology that dwells into the mysteries of parasitic, fungal lifestyles. Among the oldest continuing scientific publications on the subject, Mycopathologia had its share of 'classic papers' since the first issue was published in 1938. An analysis of the eight decades of notable contributions reveals many facets of host-pathogen interactions among 183 volumes comprising about 6885 articles. We have analyzed the impact and relevance of this body of work using a combination of citation tools (Google Scholar and Scopus) since no single citation metric gives an inclusive perspective. Among the highly cited Mycopathologia publications, those on experimental mycology accounted for the major part of the articles (36%), followed by diagnostic mycology (16%), ecology and epidemiology (15%), clinical mycology (14%), taxonomy and classification (10%), and veterinary mycology (9%). The first classic publication, collecting nearly 200 citations, appeared in 1957, while two articles published in 2010 received nearly 150 citations each, which is notable for a journal covering a highly specialized field of study. An empirical analysis of the publication trends suggests continuing interests in novel diagnostics, fungal pathogenesis, review of clinical diseases especially with relevance to the laboratory scientists, taxonomy and classification of fungal pathogens, fungal infections and carriage in pets and wildlife, and changing ecology and epidemiology of fungal diseases around the globe. We anticipate that emerging and re-emerging fungal pathogens will continue to cause significant health burden in the coming decades. It remains vital that scientists and physicians continue to collaborate by learning each other's language for the study of fungal diseases, and Mycopathologia will strive to be their partner in this increasingly important endeavor to its 100th anniversary in 2038 and beyond.

Plant phenolics and terpenoids as adjuvants of antibacterial and antifungal drugs

BACKGROUND

The intensive use of antibacterial and antifungal drugs has dramatically increased the microbial resistance and has led to a higher number of difficult-to-eradicate infections. Combination therapy with two or more antimicrobial drugs has emerged some years ago to overcome the issue, but it has proven to be not completely effective. Natural secondary metabolites of MW ≤ 500 represent promising adjuvants for antimicrobials and have been the object of several researches that have increased in the last two decades.

PURPOSE

The purpose of this Review is to do a literature search of the natural compounds that showed high enhancing capacity of antibacterials' and antifungals' effects against planktonic bacteria and fungi and to analyze which are the natural products most used in combination with a focus on polyphenols and terpenoids.

RESULTS

One hundred of papers were collected for reviewing. Fifty six (56) of them deal with combinations of low MW natural products with antibacterial drugs against planktonic bacteria and forty four (44) on natural products with antifungal drugs against planktonic fungi. Of the antibacterial adjuvants, 41 (73%) were either polyphenols (27; 48%) or terpenes (14; 25%). The remaining 15 papers (27%), deal with different class of natural products. Since most natural potentiators belong to the terpene or phenolic structural types, a more detailed description of the works dealing with these type of compounds is provided here. Bacterial and fungal resistance mechanisms, the modes of action of the main classes of antibacterial and antifungal drugs and the methodologies most used to assess the type of interactions in the combinations were included in the Review too.

CONCLUSIONS AND PERSPECTIVES

Several promising results on the potentiation effects of antifungals' and antibacterials' activities by low MW natural products mainly on polyphenols and terpenes were reported in the literature and, in spite of that most works included only in vitro assays, this knowledge opens a wide range of possibilities for the combination antimicrobial therapy. Further research including in vivo assays and clinical trials are required to determine the relevance of these antimicrobial enhancers in the clinical area and should be the focus of future studies in order to develop new antimicrobial combination agents that overpass the drawbacks of the existing antibiotics and antifungals in clinical use.

Antifungal effects of phytocompounds on Candida species alone and in combination with fluconazole

Invasive fungal infections caused by Candida spp. remain the most predominant nosocomial fungal infections. Owing to the increased use of antifungal agents, resistance of Candida spp. to antimycotics has emerged frequently, especially to fluconazole (FLC). To cope with this issue, new efforts have been dedicated to discovering novel antimycotics or new agents that can enhance the susceptibility of Candida spp. to existing antimycotics. The secondary metabolites of plants represent a large library of compounds that are important sources for new drugs or compounds suitable for further modification. Research on the anti-Candida activities of phytocompounds has been carried out in recent years and the results showed that a series of phytocompounds have anti-Candida properties, such as phenylpropanoids, flavonoids, terpenoids and alkaloids. Among these phytocompounds, some displayed potent antifungal activity, with minimum inhibitory concentrations (MICs) of ≤8 µg/mL, and several compounds were even more effective against drug-resistant Candida spp. than FLC or itraconazole (e.g. honokiol, magnolol and shikonin). Interestingly, quite a few phytocompounds not only displayed anti-Candida activity alone but also synergised with FLC against Candida spp., even leading to a reversal of FLC resistance. This review focuses on summarising the anti-Candida activities of phytocompounds as well as the interactions of phytocompounds with FLC. In addition, we briefly overview the synergistic mechanisms and present the structure of the antimycotic phytocompounds. Hopefully, this analysis will provide insight into antifungal agent discovery and new approaches against antifungal drug resistance.

Comparison of the therapeutic effects of Garcin(®) and fluconazole on Candida vaginitis

INTRODUCTION

This study aimed to determine and compare the effects of garlic tablets (Garcin(®)) and fluconazole on Candida vaginitis in women who presented to a health centre in Koohdasht, Iran, from August 2011 to March 2012.

METHODS

The clinical trial was conducted on 110 married women (aged 18-44 years) who had complaints of itching or a burning sensation in the vaginal area. Candida vaginitis was diagnosed by pH measurement of vaginal secretions, direct microscopic evaluation and Sabouraud dextrose agar cultures of the vaginal discharge. On confirmation of diagnosis, the patients were randomly divided into two groups (n = 55). One group received 1,500 mg of Garcin tablets daily and the other received fluconazole tablets 150 mg daily, over a period of seven days. Four to seven days after the completion of treatment, patients were examined for treatment response and possible side effects.

RESULTS

Complaints related to the disease improved by about 44% in the Garcin group and 63.5% in the fluconazole group (p < 0.05). The overall symptoms of the disease (i.e. redness of vulva and vagina, cheesy discharge, pustulopapular lesions and abnormal cervix) improved by about 60% in the Garcin group and 71.2% in the fluconazole group (p > 0.05). Results of microscopic evaluation and vaginal discharge culture showed significant differences before and after intervention in both groups (p < 0.05).

CONCLUSION

The present study shows that Garcin tablets could be a suitable alternative to fluconazole for the treatment of Candida vaginitis.

Potent Synergy between Spirocyclic Pyrrolidinoindolinones and Fluconazole against Candida albicans

A spiroindolinone, (1S,3R,3aR,6aS)-1-benzyl-6'-chloro-5-(4-fluorophenyl)-7'-methylspiro[1,2,3a,6a-tetrahydropyrrolo[3,4-c]pyrrole-3,3'-1H-indole]-2',4,6-trione, was previously reported to enhance the antifungal effect of fluconazole against Candida albicans. A diastereomer of this compound was synthesized, along with various analogues. Many of the compounds were shown to enhance the antifungal effect of fluconazole against C. albicans, some with exquisite potency. One spirocyclic piperazine derivative, which we have named synazo-1, was found to enhance the effect of fluconazole with an EC50 value of 300 pM against a susceptible strain of C. albicans and going as low as 2 nM against some resistant strains. Synazo-1 exhibits true synergy with fluconazole, with an FIC index below 0.5 in the strains tested. Synazo-1 exhibited low toxicity in mammalian cells relative to the concentrations required for antifungal synergy.

Influence of pH, concentration and light on stability of allicin in garlic (Allium sativum L.) aqueous extract as measured by UPLC

BACKGROUND

Garlic is one of the most important bulb vegetables and is mainly used as a spice or flavoring agent for foods. It is also cultivated for its medicinal properties, attributable to sulfur compounds, of which allicin is the most important. However, the stability of allicin in garlic extract is not well understood. In this study, using UPLC, the stability of allicin extracted in water from garlic was evaluated in phosphate buffer at different temperatures under light and dark conditions.

RESULTS

At room temperature, allicin in aqueous extract was most stable at pH 5-6 but degraded quickly at lower or higher pH. It began to degrade within 0.5 h and was not detectable after 2 h when the pH was higher than 11 or lower than 1.5. It degraded quickly when the temperature was higher than 40 °C and especially higher than 70 °C. At room temperature, allicin in water could be stored for 5 days without obvious degradation. Higher concentrations of allicin in solution were somewhat more stable than low concentrations.

CONCLUSION

Allicin extract was sensitive to pH and temperature of storage but not to light. Higher-concentration allicin solution was more stable.

Propolis Is an Efficient Fungicide and Inhibitor of Biofilm Production by Vaginal Candida albicans

Vulvovaginal candidiasis (VVC) is one of the most common genital infections in women. The therapeutic arsenal remains restricted, and some alternatives to VVC treatment are being studied. The present study evaluated the influence of a propolis extractive solution (PES) on biofilm production by Candida albicans isolated from patients with VVC. Susceptibility testing was used to verify the minimum inhibitory concentration (MIC) of PES, with fluconazole and nystatin as controls. The biofilm formation of 29 vaginal isolates of C. albicans and a reference strain that were exposed to PES was evaluated using crystal violet staining. Colony-forming units were evaluated, proteins and carbohydrates of the matrix biofilm were quantified, and scanning electron microscopy was performed. The MIC of PES ranged from 68.35 to 546.87 μg/mL of total phenol content in gallic acid. A concentration of 546.87 μg/mL was able to cause the death of 75.8% of the isolates. PES inhibited biofilm formation by C. albicans from VVC. Besides antifungal activity, PES appears to present important antibiofilm activity on abiotic surfaces, indicating that it may have an additional beneficial effect in the treatment of VVC.

Quantitative and qualitative analysis of the antifungal activity of allicin alone and in combination with antifungal drugs

The antifungal activity of allicin and its synergistic effects with the antifungal agents flucytosine and amphotericin B (AmB) were investigated in Candida albicans (C. albicans). C. albicans was treated with different conditions of compounds alone and in combination (allicin, AmB, flucytosine, allicin + AmB, allicin + flucytosine, allicin + AmB + flucytosine). After a 24-hour treatment, cells were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM) to measure morphological and biophysical properties associated with cell death. The clearing assay was conducted to confirm the effects of allicin. The viability of C. albicans treated by allicin alone or with one antifungal drug (AmB, flucytosine) in addition was more than 40% after a 24-hr treatment, but the viability of groups treated with combinations of more than two drugs was less than 32%. When the cells were treated with allicin alone or one type of drug, the morphology of the cells did not change noticeably, but when cells were treated with combinations of drugs, there were noticeable morphological changes. In particular, cells treated with allicin + AmB had significant membrane damage (burst or collapsed membranes). Classification of cells according to their cell death phase (CDP) allowed us to determine the relationship between cell viability and treatment conditions in detail. The adhesive force was decreased by the treatment in all groups compare to the control. Cells treated with AmB + allicin had a greater adhesive force than cells treated with AmB alone because of the secretion of molecules due to collapsed membranes. All cells treated with allicin or drugs were softer than the control cells. These results suggest that allicin can reduce MIC of AmB while keeping the same efficacy.

Comparison between allicin and fluconazole in Candida albicans biofilm inhibition and in suppression of HWP1 gene expression

Candida albicans is an opportunistic human pathogen with the ability to differentiate and grow in filamentous forms and exist as biofilms. The biofilms are a barrier to treatment as they are often resistant to the antifungal drugs. In this study, we investigated the antifungal activity of allicin, an active compound of garlic on various isolates of C. albicans. The effect of allicin on biofilm production in C. albicans as compared to fluconazole, an antifungal drug, was investigated using the tetrazolium (XTT) reduction-dependent growth and crystal violet assays as well as scanning electron microscopy (SEM). Allicin-treated cells exhibited significant reduction in biofilm growth (p<0.05) compared to fluconazole-treated and also growth control cells. Moreover, observation by SEM of allicin and fluconazole-treated cells confirmed a dose-dependent membrane disruption and decreased production of organisms. Finally, the expression of selected genes involved in biofilm formation such as HWP1 was evaluated by semi-quantitative RT-PCR and relative real time RT-PCR. Allicin was shown to down-regulate the expression of HWP1.

Quantitative and qualitative analyses of the cell death process in Candida albicans treated by antifungal agents

The death process of Candida albicans was investigated after treatment with the antifungal agents flucytosine and amphotericin B by assessing morphological and biophysical properties associated with cell death. C. albicans was treated varying time periods (from 6 to 48 hours) and examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM and AFM images clearly showed changes in morphology and biophysical properties. After drug treatment, the membrane of C. albicans was perforated, deformed, and shrunken. Compared to the control, C. albicans treated with flucytosine was softer and initially showed a greater adhesive force. Conversely, C. albicans treated with amphotericin B was harder and had a lower adhesive force. In both cases, the surface roughness increased as the treatment time increased. The relationships between morphological changes and the drugs were observed by AFM clearly; the surface of C. albicans treated with flucytosine underwent membrane collapse, expansion of holes, and shrinkage, while the membranes of cells treated with amphotericin B peeled off. According to these observations, the death process of C. albicans was divided into 4 phases, CDP₀, CDP₁, CDP₂, and CDP₄, which were determined based on morphological changes. Our results could be employed to further investigate the antifungal activity of compounds derived from natural sources.

Anti-candidal activity of essential oils alone and in combination with amphotericin B or fluconazole against multi-drug resistant isolates of Candida albicans

Therapy for candidiasis is becoming problematic due to the toxicities of currently available antifungal agents and the increasing prevalence of resistance among the etiologic agents. Therefore, new antifungals and alternative approaches are needed. In this study, 20 fluconazole-resistant strains of Candida albicans were found to have varying levels of resistance to other azoles, i.e., itraconazole (MIC of 4-128 μg/ml) and ketoconazole (2-256 μg/ml). In addition, 13 of these isolates appeared resistant to amphotericin B (32-128 μg/ml). A total of 21 plant essential oils were screened for their antifungal activity against these multi-drug resistant isolates. The oils of Cymbopogon martini, i.e., citral and cinnamaldehyde, exhibited strong inhibitory activity with minimum inhibitory concentrations (MIC(50)) ranging from 90-100 μg/ml. The test oils were more effective than fluconazole and amphotericin B in inhibiting azole- and amphotericin B-resistant, as well as amphotericin B-susceptible isolates. The test oils and especially eugenol, exhibited significant synergy with fluconazole or amphotericin B against the test isolates. These findings suggest the possible effective use of certain oils alone or in combination with fluconazole or amphotericin B, against multi-drug resistant isolates of C. albicans.

Comparison between efficacy of allicin and fluconazole against Candida albicans in vitro and in a systemic candidiasis mouse model

The efficacy of allicin compared with fluconazole in alleviating systemic Candida albicans infections was evaluated both in vitro and in vivo through a systemic candidiasis mouse model. Determination of in vitro minimum inhibitory concentrations (MICs) for different C. albicans isolates revealed that both allicin and fluconazole showed different MICs that ranged from 0.05 to 12.5 μg mL(-1) and 0.25 to 16 μg mL(-1) , respectively. A time-kill study showed a significant effect of allicin (P<0.01) against C. albicans, comparable to that of fluconazole. Scanning electron microscopy observation revealed that, similar to fluconazole, allicin produced structural destruction of C. albicans cell surface at low MIC and lysis or puncture at high MIC concentrations. Treatment of BALB/c mice systemically infected with C. albicans showed that although the allicin treatment (at 5 mg kg(-1) day(-1) ) was slightly less efficacious than fluconazole treatment in terms of the fungal load reduction and host survival time, it was still effective against C. albicans in terms of mean survival time, which increased from 8.4 to 15.8 days. These results demonstrate the efficacy of anticandidal effects of allicin both in vitro and in an animal model of candidiasis and affirm the potential of allicin as an adjuvant therapy to fluconazole.