EDTA as an adjunct antifungal agent for invasive pulmonary aspergillosis in a rodent model

The antimicrobial and immunomodulatory effects of Ionophores for the treatment of human infection

Ionophores are a diverse class of synthetic and naturally occurring ion transporter compounds which demonstrate both direct and in-direct antimicrobial properties against a broad panel of bacterial, fungal, viral and parasitic pathogens. In addition, ionophores can regulate the host-immune response during communicable and non-communicable disease states. Although the clinical use of ionophores such as Amphotericin B, Bedaquiline and Ivermectin highlight the utility of ionophores in modern medicine, for many other ionophore compounds issues surrounding toxicity, bioavailability or lack of in vivo efficacy studies have hindered clinical development. The antimicrobial and immunomodulating properties of a range of compounds with characteristics of ionophores remain largely unexplored. As such, ionophores remain a latent therapeutic avenue to address both the global burden of antimicrobial resistance, and the unmet clinical need for new antimicrobial therapies. This review will provide an overview of the broad-spectrum antimicrobial and immunomodulatory properties of ionophores, and their potential uses in clinical medicine for combatting infection.

Type I Interferons Ameliorate Zinc Intoxication of Candida glabrata by Macrophages and Promote Fungal Immune Evasion

Host and fungal pathogens compete for metal ion acquisition during infectious processes, but molecular mechanisms remain largely unknown. Here, we show that type I interferons (IFNs-I) dysregulate zinc homeostasis in macrophages, which employ metallothionein-mediated zinc intoxication of pathogens as fungicidal response. However, Candida glabrata can escape immune surveillance by sequestering zinc into vacuoles. Interestingly, zinc-loading is inhibited by IFNs-I, because a Janus kinase 1 (JAK1)-dependent suppression of zinc homeostasis affects zinc distribution in macrophages as well as generation of reactive oxygen species (ROS). In addition, systemic fungal infections elicit IFN-I responses that suppress splenic zinc homeostasis, thereby altering macrophage zinc pools that otherwise exert fungicidal actions. Thus, IFN-I signaling inadvertently increases fungal fitness both in vitro and in vivo during fungal infections. Our data reveal an as yet unrecognized role for zinc intoxication in antifungal immunity and suggest that interfering with host zinc homeostasis may offer therapeutic options to treat invasive fungal infections.

Targeting Pseudomonas aeruginosa in the Sputum of Primary Ciliary Dyskinesia Patients with a Combinatorial Strategy Having Antibacterial and Anti-Virulence Potential

In primary ciliary dyskinesia (PCD) patients, Pseudomonas aeruginosa is a major opportunistic pathogen, frequently involved in chronic infections of the lower airways. Infections by this bacterial species correlates with a worsening clinical prognosis and recalcitrance to currently available therapeutics. The antimicrobial peptide, lin-SB056-1, in combination with the cation chelator ethylenediaminetetraacetic acid (EDTA), was previously demonstrated to be bactericidal against P. aeruginosa in an artificial sputum medium. The purpose of this study was to validate the anti-P. aeruginosa activity of such a combination in PCD sputum and to evaluate the in vitro anti-virulence effects of EDTA. In combination with EDTA, lin-SB056-1 was able to significantly reduce the load of endogenous P. aeruginosa ex vivo in the sputum of PCD patients. In addition, EDTA markedly reduced the production of relevant bacterial virulence factors (e.g., pyocyanin, proteases, LasA) in vitro by two representative mucoid strains of P. aeruginosa isolated from the sputum of PCD patients. These results indicate that the lin-SB056-1/EDTA combination may exert a dual antimicrobial and anti-virulence action against P. aeruginosa, suggesting a therapeutic potential against chronic airway infections sustained by this bacterium.

A Novel Polyaminocarboxylate Compound To Treat Murine Pulmonary Aspergillosis by Interfering with Zinc Metabolism

Aspergillus fumigatus can cause pulmonary aspergillosis in immunocompromised patients and is associated with a high mortality rate due to a lack of reliable treatment options. This opportunistic pathogen requires zinc in order to grow and cause disease. Novel compounds that interfere with fungal zinc metabolism may therefore be of therapeutic interest. We screened chemical libraries containing 59,223 small molecules using a resazurin assay that compared their effects on an A. fumigatus wild-type strain grown under zinc-limiting conditions and on a zinc transporter knockout strain grown under zinc-replete conditions to identify compounds affecting zinc metabolism. After a first screen, 116 molecules were selected whose inhibitory effects on fungal growth were further tested by using luminescence assays and hyphal length measurements to confirm their activity, as well as by toxicity assays on HeLa cells and mice. Six compounds were selected following a rescreening, of which two were pyrazolones, two were porphyrins, and two were polyaminocarboxylates. All three groups showed good in vitro activity, but only one of the polyaminocarboxylates was able to significantly improve the survival of immunosuppressed mice suffering from pulmonary aspergillosis. This two-tier screening approach led us to the identification of a novel small molecule with in vivo fungicidal effects and low murine toxicity that may lead to the development of new treatment options for fungal infections by administration of this compound either as a monotherapy or as part of a combination therapy.

Novel Zinc-Attenuating Compounds as Potent Broad-Spectrum Antifungal Agents with In Vitro and In Vivo Efficacy

An increase in the incidence of rare but hard-to-treat invasive fungal pathogens as well as resistance to the currently available antifungal drugs calls for new broad-spectrum antifungals with a novel mechanism of action. Here we report the identification and characterization of two novel zinc-attenuating compounds, ZAC307 and ZAC989, which exhibit broad-spectrum in vitro antifungal activity and in vivo efficacy in a fungal kidney burden candidiasis model. The compounds were identified serendipitously as part of a drug discovery process aimed at finding novel inhibitors of the fungal plasma membrane proton ATPase Pma1. Based on their structure, we hypothesized that they might act as zinc chelators. Indeed, both fluorescence-based affinity determination and potentiometric assays revealed these compounds, subsequently termed zinc-attenuating compounds (ZACs), to have strong affinity for zinc, and their growth inhibitory effects on Candida albicans and Aspergillus fumigatus could be inactivated by the addition of exogenous zinc to fungal growth media. We determined the ZACs to be fungistatic, with a low propensity for resistance development. Gene expression analysis suggested that the ZACs interfere negatively with the expression of genes encoding the major components of the A. fumigatus zinc uptake system, thus supporting perturbance of zinc homeostasis as the likely mode of action. With demonstrated in vitro and in vivo antifungal activity, low propensity for resistance development, and a novel mode of action, the ZACs represent a promising new class of antifungal compounds, and their advancement in a drug development program is therefore warranted.

The Semi-Synthetic Peptide Lin-SB056-1 in Combination with EDTA Exerts Strong Antimicrobial and Antibiofilm Activity against Pseudomonas aeruginosa in Conditions Mimicking Cystic Fibrosis Sputum

Pseudomonas aeruginosa is a major cause of chronic lung infections in cystic fibrosis (CF) patients. The ability of the bacterium to form biofilms and the presence of a thick and stagnant mucus in the airways of CF patients largely contribute to antibiotic therapy failure and demand for new antimicrobial agents able to act in the CF environment. The present study investigated the anti-P. aeruginosa activity of lin-SB056-1, a recently described semi-synthetic antimicrobial peptide, used alone and in combination with the cation chelator ethylenediaminetetraacetic acid (EDTA). Bactericidal assays were carried out in standard culture conditions and in an artificial sputum medium (ASM) closely resembling the CF environment. Peptide’s structure and interaction with large unilamellar vesicles in media with different ionic strengths were also investigated through infrared spectroscopy. Lin-SB056-1 demonstrated fast and strong bactericidal activity against both mucoid and non-mucoid strains of P. aeruginosa in planktonic form and, in combination with EDTA, caused significant reduction of the biomass of P. aeruginosa mature biofilms. In ASM, the peptide/EDTA combination exerted a strong bactericidal effect and inhibited the formation of biofilm-like structures of P. aeruginosa. Overall, the results obtained highlight the potential of the lin-SB056-1/EDTA combination for the treatment of P. aeruginosa lung infections in CF patients.

Rodent Models of Invasive Aspergillosis due to Aspergillus fumigatus: Still a Long Path toward Standardization

Invasive aspergillosis has been studied in laboratory by the means of plethora of distinct animal models. They were developed to address pathophysiology, therapy, diagnosis, or miscellaneous other concerns associated. However, there are great discrepancies regarding all the experimental variables of animal models, and a thorough focus on them is needed. This systematic review completed a comprehensive bibliographic analysis specifically-based on the technical features of rodent models infected with Aspergillus fumigatus. Out the 800 articles reviewed, it was shown that mice remained the preferred model (85.8% of the referenced reports), above rats (10.8%), and guinea pigs (3.8%). Three quarters of the models involved immunocompromised status, mainly by steroids (44.4%) and/or alkylating drugs (42.9%), but only 27.7% were reported to receive antibiotic prophylaxis to prevent from bacterial infection. Injection of spores (30.0%) and inhalation/deposition into respiratory airways (66.9%) were the most used routes for experimental inoculation. Overall, more than 230 distinct A. fumigatus strains were used in models. Of all the published studies, 18.4% did not mention usage of any diagnostic tool, like histopathology or mycological culture, to control correct implementation of the disease and to measure outcome. In light of these findings, a consensus discussion should be engaged to establish a minimum standardization, although this may not be consistently suitable for addressing all the specific aspects of invasive aspergillosis.

Metal Chelation as a Powerful Strategy to Probe Cellular Circuitry Governing Fungal Drug Resistance and Morphogenesis

Fungal pathogens have evolved diverse strategies to sense host-relevant cues and coordinate cellular responses, which enable virulence and drug resistance. Defining circuitry controlling these traits opens new opportunities for chemical diversity in therapeutics, as the cognate inhibitors are rarely explored by conventional screening approaches. This has great potential to address the pressing need for new therapeutic strategies for invasive fungal infections, which have a staggering impact on human health. To explore this approach, we focused on a leading human fungal pathogen, Candida albicans, and screened 1,280 pharmacologically active compounds to identify those that potentiate the activity of echinocandins, which are front-line therapeutics that target fungal cell wall synthesis. We identified 19 compounds that enhance activity of the echinocandin caspofungin against an echinocandin-resistant clinical isolate, with the broad-spectrum chelator DTPA demonstrating the greatest synergistic activity. We found that DTPA increases susceptibility to echinocandins via chelation of magnesium. Whole genome sequencing of mutants resistant to the combination of DTPA and caspofungin identified mutations in the histidine kinase gene NIK1 that confer resistance to the combination. Functional analyses demonstrated that DTPA activates the mitogen-activated protein kinase Hog1, and that NIK1 mutations block Hog1 activation in response to both caspofungin and DTPA. The combination has therapeutic relevance as DTPA enhanced the efficacy of caspofungin in a mouse model of echinocandin-resistant candidiasis. We found that DTPA not only reduces drug resistance but also modulates morphogenesis, a key virulence trait that is normally regulated by environmental cues. DTPA induced filamentation via depletion of zinc, in a manner that is contingent upon Ras1-PKA signaling, as well as the transcription factors Brg1 and Rob1. Thus, we establish a new mechanism by which metal chelation modulates morphogenetic circuitry and echinocandin resistance, and illuminate a novel facet to metal homeostasis at the host-pathogen interface, with broad therapeutic potential.

Invasive fungal infections pose a serious threat to human health worldwide, with Candida albicans being a leading fungal pathogen. Mortality is in part due to the limited arsenal of effective antifungals, with drug resistance on the rise. The echinocandins, which target the fungal cell wall, are the newest class of antifungal, and echinocandin resistance has already emerged. Here, we screened a library of 1,280 pharmacologically active compounds to identify those that potentiate echinocandin activity against an echinocandin-resistant isolate. The lead compound was a chelator, DTPA, which affects resistance by depleting magnesium. Genome sequencing of mutants resistant to the combination of DTPA and echinocandin revealed mutations in the gene encoding Nik1, which signals upstream of the Hog1 stress response pathway. We established that DTPA acts through Nik1 to modulate Hog1 signaling and enhance echinocandin activity, and that this combination has therapeutic benefits in a murine model of candidiasis. We also discovered that DTPA modulates C. albicans morphogenesis, a key virulence trait. DTPA induced filamentation by chelating zinc, in a manner that is contingent upon core filamentation pathways and specialized circuitry. Thus, we establish novel roles for metal homeostasis in C. albicans pathogenesis, thereby illuminating new therapeutic strategies for life-threatening infectious disease.

In vitro and in vivo activity of EDTA and antibacterial agents against the biofilm of mucoid Pseudomonas aeruginosa

PURPOSE

Refractory infection caused by bacterial biofilm is an important clinical problem. Pseudomonas aeruginosa is a common pathogen responsible for persistent and chronic biofilm infections. We aimed to explore the in vitro and in vivo activity of ethylenediamine tetraacetic acid (EDTA) in combination with antibacterial agents against mucoid P. aeruginosa biofilm.

METHODS

The minimal inhibitory concentration (MIC) and minimal bactericidal concentration of ciprofloxacin, gentamicin, and ampicillin alone or with EDTA against P. aeruginosa were determined in vitro. Extracellular polysaccharides (EPS) and structural parameters of the biofilm were monitored. P. aeruginosa was aerosolized and delivered into the lungs of guinea pigs, which were treated with ciprofloxacin with or without EDTA. The colony-forming units (CFUs) of P. aeruginosa were determined from the lungs.

RESULTS

EDTA reduced the MIC of ciprofloxacin and ampicillin by about 30-fold and that of gentamicin by twofold. EDTA reduced the biofilm EPS and the proportion of viable bacteria. The thickness, average diffusion distance, and textural entropy of EDTA-treated biofilm were significantly decreased. EDTA plus antibiotics reduced the colony counting from 10⁷ to 10³ CFU/mL. In vivo, EDTA plus ciprofloxacin had a significantly lower mean CFU/g of lung tissue (EDTA + ciprofloxacin 1.3 ± 0.19; EDTA 4.4 ± 0.57; ciprofloxacin 4.2 ± 0.47), and lung lesions were less severe compared with the single treatment groups.

CONCLUSIONS

EDTA can destroy the biofilm structures of mucoid P. aeruginosa in vitro. Moreover, EDTA and ciprofloxacin had a significant bactericidal effect against biofilm in vivo.

Targeting zinc homeostasis to combat Aspergillus fumigatus infections

Aspergillus fumigatus is able to invade and grow in the lungs of immunosuppressed individuals and causes invasive pulmonary aspergillosis. The concentration of free zinc in living tissues is much lower than that required for optimal fungal growth in vitro because most of it is tightly bound to proteins. To obtain efficiently zinc from a living host A. fumigatus uses the zinc transporters ZrfA, ZrfB, and ZrfC. The ZafA transcriptional regulator induces the expression of all these transporters and is essential for virulence. Thus, ZafA could be targeted therapeutically to inhibit fungal growth. The ZrfC transporter plays the major role in zinc acquisition from the host whereas ZrfA and ZrfB rather have a supplementary role to that of ZrfC. In addition, only ZrfC enables A. fumigatus to overcome the inhibitory effect of calprotectin, which is an antimicrobial Zn/Mn-chelating protein synthesized and released by neutrophils within the fungal abscesses of immunosuppressed non-leucopenic animals. Hence, fungal survival in these animals would be undermined upon blocking therapeutically the function of ZrfC. Therefore, both ZafA and ZrfC have emerged as promising targets for the discovery of new antifungals to treat Aspergillus infections.

Presence of Candida albicans in Root Canals of Teeth with Apical Periodontitis and Evaluation of their Possible Role in Failure of Endodontic Treatment

BACKGROUND

Candidal organisms are commensals of the oral cavity and their opportunistic infection depends on the interplay of local and systemic factors. Endodontic treatment failure has been associated with the persistence of microbial flora following therapy in the root canal system, and this includes fungi like Candida, which are resistant to conventional root canal irrigants.

MATERIALS AND METHODS

A total of 20 mandibular molars were included in the study of which 15 were primary randomized controlled trial cases, whereas 5 were retreatment cases. The patient's saliva, as well as the root canal flora, were examined for the presence of Candida organisms and further confirmed for the presence of Candida albicans.

RESULTS

Of the 20 samples comprising the study group, the saliva culture revealed 11 of them to have a colony forming unit (CFU) >400 and 9 of the 20 canals microbiology showed CFU >400. Among the 15 first-time root canal treatment cases, saliva examination these revealed 8 of them to have CFU >400 and the canal microbiology of these showed 6 of them to have CFU >400. Among the retreatment cases, 3 of the 5 cases showed CFU >400 in both the saliva DN canal culture.

CONCLUSION

Candidal contamination of the root canals could be the cause of endodontic treatment failure and thus emphasizes the importance of rubber dam isolation and the use of irrigants with antifungal properties for sufficient duration during treatment.

Zinc acquisition: a key aspect in Aspergillus fumigatus virulence

Zinc is an essential micronutrient required for the growth of all microorganisms. To grow in the lungs of a susceptible patient Aspergillus fumigatus must obtain zinc from the surrounding tissues. The concentration of Zn(2+) ions in living tissues is much lower than that required for optimal fungal growth in vitro because most of them are tightly bound to proteins at the physiological pH. However, A. fumigatus has several zinc transporters (ZrfA, ZrfB and ZrfC) that enable it to uptake zinc efficiently under the extreme zinc-limiting conditions provided by a susceptible host. The ZafA transcriptional regulator induces the expression of these transporters and is essential for virulence. ZrfC is required for fungal growth within the host tissues, whereas ZrfA and ZrfB play an accessory role. The zinc-scavenging capacity of ZrfC relies on its unusually long N-terminus. In addition, ZrfC also enables A. fumigatus to overcome the inhibitory effect of calprotectin, which is an antimicrobial Zn/Mn-chelating protein synthesized in high amounts by neutrophils, even in immunosuppressed non-leucopenic animals. In summary, the regulation of zinc homeostasis and zinc acquisition could be promising targets for the discovery and development of a new generation of antifungals for the treatment of invasive pulmonary aspergillosis.

HapX-mediated adaption to iron starvation is crucial for virulence of Aspergillus fumigatus

Iron is essential for a wide range of cellular processes. Here we show that the bZIP-type regulator HapX is indispensable for the transcriptional remodeling required for adaption to iron starvation in the opportunistic fungal pathogen Aspergillus fumigatus. HapX represses iron-dependent and mitochondrial-localized activities including respiration, TCA cycle, amino acid metabolism, iron-sulfur-cluster and heme biosynthesis. In agreement with the impact on mitochondrial metabolism, HapX-deficiency decreases resistance to tetracycline and increases mitochondrial DNA content. Pathways positively affected by HapX include production of the ribotoxin AspF1 and siderophores, which are known virulence determinants. Iron starvation causes a massive remodeling of the amino acid pool and HapX is essential for the coordination of the production of siderophores and their precursor ornithine. Consistent with HapX-function being limited to iron depleted conditions and A. fumigatus facing iron starvation in the host, HapX-deficiency causes significant attenuation of virulence in a murine model of aspergillosis. Taken together, this study demonstrates that HapX-dependent adaption to conditions of iron starvation is crucial for virulence of A. fumigatus.

Due to its requirement for a wide range of cellular processes, iron is an essential nutrient for virtually every organism. The mammalian immune system utilizes iron-withholding mechanisms to deny access to free iron. Therefore, pathogens must overcome extreme iron limitation. Patients with suppressed immune systems due to cancer treatments, organ transplantation, or genetic disorders are at high risk of infection with the ubiquitously present fungal pathogen Aspergillus fumigatus. In this study we found that in Aspergillus fumigatus iron starvation results in drastic metabolic changes depending on the transcription factor HapX. During iron starvation, HapX functions include the repression of iron-consuming pathways to spare iron and activation of iron uptake by siderophores. Siderophores are small molecules able to “steal” iron from host molecules and have previously been shown to play a crucial role in the virulence of Aspergillus fumigatus. Genetic inactivation of HapX attenuates virulence of Aspergillus fumigatus in a murine model of aspergillosis, demonstrating that adaption to iron limitation is a crucial virulence determinant. The identification of numerous HapX-affected genes with a yet uncharacterized link to iron will aid in the further characterization of the metabolic pathways required for fungal adaption to iron starvation and virulence traits.

Silver enhances the in vitro antifungal activity of the saponin, CAY-1

The fungicidal properties of purified CAY-1, dissolved silver ion and ethylenediamine tetraacetic acid (EDTA) separately were studied in vitro as were the abilities of silver and EDTA to enhance CAY-1 fungicidal properties. Non-germinated and germinating conidia of Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger, Fusarium verticillioides (Fusarium moniliforme), Fusarium oxysporum and Fusarium solani were incubated separately with CAY-1 (0-24.8 μg ml(-1)), silver (0-111.1 μg ml(-1)), and EDTA (0-2400 μg ml(-1)). Controls consisted of non-germinated or germinated conidia in test medium. To assess combined activity, compounds, based on the sub-lethal doses of each as defined in the initial experiments, were combined and tested in bioassays. Controls for the mixed sets consisted of non-germinated or germinated conidia only or with the sub-lethal CAY-1 test concentrations. The minimum inhibitory concentrations (MICs) for CAY-1 and silver, both separate and combined, were determined. Viability assays showed CAY-1 activity only against the germinating conidia of A. flavus, A. niger and F. solani. Silver was active against the germinating conidia of all fungi and the non-germinated conidia of F. oxysporum and F. solani. Combined silver and CAY-1 produced significant viability loss at concentrations not effective separately. EDTA was not fungicidal separately and did not enhance CAY-1 fungicidal properties. MIC data showed that CAY-1 plus silver had an additive effect. Results indicate that dissolved silver was fungicidal in vitro and enhanced the fungicidal properties of CAY-1 at concentrations ineffective when tested separately.

In vitro and ex vivo assays of virulence in Candida albicans

The measurement of virulence using ex vivo and in vitro models is discussed in the context of the human pathogenic yeast, Candida albicans. The models described are of two types. First, reconstituted tissues of various sorts are used that are derived from human carcinomas. The tissues are grown in vitro in complex media, attain a three-dimensional tissue structure, and retain cell-surface antigens typical of the specific tissue. Both adherence and invasion of tissues can be studied following infection with strains of C. albicans (1, 2). Further, one can increase the level of complexity by providing infected tissues with host phagocytes or cytokines such that an immune contribution to protection can be followed (3-5). The second model employs Drosophila melanogaster larvae that are infected with C. albicans (6). In this model, the progression of virulence is followed after injection of strains of a pathogen of interest into the fly abdomen. Thus, in the case of human pathogenic fungi, the recognition of host tissues and invasion by the specific pathogen can be studied in vitro and correlations developed for human disease. The obvious advantage to using animal models (e.g., mice) is reduced cost, such that large numbers of C. albicans strains can be assessed for their virulence properties. Additionally, another application of these models is in drug discovery. It is clear that there are both advantages and disadvantages of the use of alternate models other than a murine model, to evaluate disease, and this is discussed below.

SreA-mediated iron regulation in Aspergillus fumigatus

Aspergillus fumigatus, the most common airborne fungal pathogen of humans, employs two high-affinity iron uptake systems: iron uptake mediated by the extracellular siderophore triacetylfusarinine C and reductive iron assimilation. Furthermore, A. fumigatus utilizes two intracellular siderophores, ferricrocin and hydroxyferricrocin, to store iron. Siderophore biosynthesis, which is essential for virulence, is repressed by iron. Here we show that this control is mediated by the GATA factor SreA. During iron-replete conditions, SreA deficiency partially derepressed synthesis of triacetylfusarinine C and uptake of iron resulting in increased cellular accumulation of both iron and ferricrocin. Genome-wide DNA microarray analysis identified 49 genes that are repressed by iron in an SreA-dependent manner. This gene set, termed SreA regulon, includes all known genes involved in iron acquisition, putative novel siderophore biosynthetic genes, and also genes not directly linked to iron metabolism. SreA deficiency also caused upregulation of iron-dependent and antioxidative pathways, probably due to the increased iron content and iron-mediated oxidative stress. Consistently, the sreA disruption mutant displayed increased sensitivity to iron, menadion and phleomycin but retained wild-type virulence in a mouse model. As all detrimental effects of sreA disruption are restricted to iron-replete conditions these data underscore that A. fumigatus faces iron-depleted conditions during infection.

Assessment of Aspergillus fumigatus burden in pulmonary tissue of guinea pigs by quantitative PCR, galactomannan enzyme immunoassay, and quantitative culture

Early diagnosis of invasive pulmonary aspergillosis is problematic in some patient groups due to the lack of rapid, sensitive, specific, and reliable diagnostic tests. Fungal burden and therapeutic efficacy were assessed by survival, quantitative culture (CFU counts), galactomannan enzyme immunoassay (GM-EIA), and quantitative PCR (qPCR) in a new guinea pig model of invasive pulmonary aspergillosis using an aerosol challenge. At 1 day postinfection, qPCR determined that the pulmonary fungal burden was 2 log(10) higher than that determined by CFU counting and increased significantly (P < 0.03) over time. In contrast, the tissue burden assessed by CFU counting did not rise over the course of the study. Therapy with the antifungal drug voriconazole produced statistically significant decreases in pulmonary fungal burden, as detected by CFU counting (P < 0.02), qPCR, and GM-EIA (both P < 0.0002). Daily assessment of the progression of fungal infection in serum was performed by qPCR and GM-EIA. GM-EIA demonstrated a statistically significant reduction in the fungal load on days 6 and 7 in voriconazole-treated animals compared to time-matched controls (P < 0.02). Confirmation of fungal tissue burden by two or more methods should provide a more precise account of the burden, allowing improved assessment of diagnostic and therapeutic strategies in invasive pulmonary aspergillosis.

Siderophores in fungal physiology and virulence

Maintaining the appropriate balance of iron between deficiency and toxicity requires fine-tuned control of systems for iron uptake and storage. Both among fungal species and within a single species, different systems for acquisition, storage, and regulation of iron are present. Here we discuss the most recent findings on the mechanisms involved in maintaining iron homeostasis with a focus on siderophores, low-molecular-mass iron chelators, employed for iron uptake and storage. Recently siderophores have been found to be crucial for pathogenicity of animal, as well as plant-pathogenic fungi and for maintenance of plant-fungal symbioses.

Factors affecting antimicrobial activity of MUC7 12-mer, a human salivary mucin-derived peptide

Background

MUC7 12-mer (RKSYKCLHKRCR), a cationic antimicrobial peptide derived from the human low-molecular-weight salivary mucin MUC7, possesses potent antimicrobial activity in vitro. In order to evaluate the potential therapeutic application of the MUC7 12-mer, we examined the effects of mono- and divalent cations, EDTA, pH, and temperature on its antimicrobial activity.

Methods

Minimal Inhibitory Concentrations (MICs) were determined using a liquid growth inhibition assay in 96-well microtiter plates. MUC7 12-mer was added at concentrations of 1.56–50 μM. MICs were determined at three endpoints: MIC-0, MIC-1, and MIC-2 (the lowest drug concentration showing 10%, 25% and 50% of growth, respectively). To examine the effect of salts or EDTA, a checkerboard microdilution technique was used. Fractional inhibitory concentration index (FICi) was calculated on the basis of MIC-0. The viability of microbial cells treated with MUC7 12-mer in the presence of sodium or potassium was also determined by killing assay or flow cytometry.

Results

The MICs of MUC7 12-mer against organisms tested ranged from 6.25–50 μM. For C. albicans, antagonism (FICi 4.5) was observed for the combination of MUC7 12-mer and calcium; however, there was synergism (FICi 0.22) between MUC7 12-mer and EDTA, and the synergism was retained in the presence of calcium at its physiological concentration (1–2 mM). No antagonism but additivity or indifference (FICi 0.55–2.5) was observed for the combination of MUC7 12-mer and each K⁺, Na⁺, Mg²⁺, or Zn²⁺. MUC7 12-mer peptide (at 25 μM) also exerted killing activity in the presence of NaCl, (up to 25 mM for C. albicans and up to 150 mM for E. coli, a physiological concentration of sodium in the oral cavity and serum, respectively) and retained candidacidal activity in the presence of KCl (up to 40 mM). The peptide exhibited higher inhibitory activity against C. albicans at pH 7, 8, and 9 than at pH 5 and 6, and temperature up to 60°C did not affect the activity.

Conclusion

MUC7 12-mer peptide is effective anticandidal agent at physiological concentrations of variety of ions in the oral cavity. These results suggest that, especially in combination with EDTA, it could potentially be applied as an alternative therapeutic agent for the treatment of human oral candidiasis.