Effects of Iron Chelators on the Formation and Development of Aspergillus fumigatus Biofilm

Resynthesis of Damaged Fe-S Cluster Proteins Protects Aspergillus fumigatus Against Oxidative Stress in the Absence of Mn-Superoxide Dismutase

The importance of manganese superoxide dismutase (Mn-SOD), an evolutionarily ancient metalloenzyme that maintains the integrity and function of mitochondria, was studied in oxidative stress-treated Aspergillus fumigatus cultures. Deletion of the Mn-SOD gene (sodB) increased both the menadione sodium bisulfite (MSB)-elicited oxidative stress and the deferiprone (DFP)-induced iron limitation stress sensitivity of the strain. Moreover, DFP treatment enhanced the MSB sensitivity of both the gene deletion mutant and the reference strain. The lack of SodB also increased the susceptibility of conidia to killing by human macrophages. Concurring with the stress sensitivity data, RNS sequencing data also demonstrated that the deletion of sodB largely altered the MSB-induced oxidative stress response. The difference between the oxidative stress responses of the two strains manifested mainly in the intensity of the response. Importantly, upregulation of "Ribosome protein", "Iron uptake", and "Fe-S cluster assembly" genes, alterations in the transcription of "Fe-S cluster protein" genes, and downregulation of "Heme binding protein" genes under MSB stress were characteristic only for the ΔsodB gene deletion mutant. We assume that the elevated superoxide level generated by MSB treatment may have destroyed Fe-S cluster proteins of mitochondria in the absence of SodB. This intensified the resynthesis of Fe-S cluster proteins, which was accompanied with enhanced translation and iron acquisition, leading to increased DFP sensitivity.

Nanoparticle-Mediated Delivery of Deferasirox: A Promising Strategy Against Invasive Aspergillosis

BACKGROUND

Invasive aspergillosis (IA) is a deadly fungal lung infection. Antifungal resistance and treatment side effects are major concerns. Iron chelators are vital for IA management, but systemic use can cause side effects. We developed nanoparticles (NPs) to selectively deliver the iron chelator deferasirox (DFX) for IA treatment.

METHODS

DFX was encapsulated in poly(lactic-co-glycolic acid) (PLGA) NPs using a single emulsion solvent evaporation method. The NPs were characterized by light scattering and electron microscopy. DFX loading efficiency and release were assessed spectrophotometrically. Toxicity was evaluated using SRB, luciferase, and XTT assays. Therapeutic efficacy was tested in an IA mouse model, assessing fungal burden by qPCR and biodistribution via imaging.

RESULTS

DFX-NPs had a size of ~50 nm and a charge of ~-30 mV, with a loading efficiency of ~80%. Release kinetics showed DFX release via diffusion and bioerosion. The EC50 of DFX-NPs was significantly lower (p < 0.001) than the free drug, and they were significantly less toxic (p < 0.0001) in mammalian cell cultures. In vivo, NP treatment significantly reduced Af burden (p < 0.05).

CONCLUSION

The designed DFX-NPs effectively target and kill Af with minimal toxicity to mammalian cells. The significant in vivo therapeutic efficacy suggests these NPs could be a safe and effective treatment for IA.

A Preliminary Study on the Effect of Deferoxamine on the Disruption of Bacterial Biofilms and Antimicrobial Resistance

Objectives

Antiviral therapy approaches have become significant strategies to combat antibiotic resistance. Metal ions, particularly iron, play crucial roles in metabolic activities and virulence of bacteria. Loading iron into siderophore molecules could potentially circumvent antimicrobial resistance. This study aimed to evaluate the antibiofilm and antimicrobial effects of deferoxamine (DFO), an iron chelator and natural siderophore, on antibiotic susceptibility in clinical methicillin-resistant Staphylococcus aureus (MRSA) and carbapenem-resistant Acinetobacter baumannii (CRAB) isolates.

Materials and Methods

The in vitro antibacterial activity of DFO alone and in combination with vancomycin [VAN (30 μg)], amoxicillin (25 μg), colistin (10 μg), and imipenem (10 μg), was investigated against MRSA and CRAB isolates using the disk diffusion method. The spectrophotometric microplate method was used to detect the in vitro antibiofilm effect of DFO.

Results

DFO exhibited a synergistic effect with VAN, amoxicillin, and colistin and significantly disrupted mature biofilm formation in MRSA and CRAB isolates. Notably, the antibiofilm effect of DFO was more pronounced in CRAB strains.

Conclusion

These findings highlight the potential of DFO as an antibiofilm agent candidate and suggest that it can enhance the antibiotic susceptibility of certain microorganism species.

Oleanolic Acid Promotes the Formation of Probiotic Escherichia coli Nissle 1917 (EcN) Biofilm by Inhibiting Bacterial Motility

Probiotic biofilms have been beneficial in the fight against infections, restoring the equilibrium of the host's gut microbiota, and enhancing host health. They are considered a novel strategy for probiotic gut colonization. In this case, we evaluated the effects of various active substances from traditional Chinese medicine on Escherichia coli Nissle 1917 (EcN) to determine if they promote biofilm formation. It was shown that 8-64 μg/mL of oleanolic acid increased the development of EcN biofilm. Additionally, we observed that oleanolic acid can effectively suppress biofilm formation in pathogenic bacteria such as Salmonella and Staphylococcus aureus. Next, we assessed the amount of EcN extracellular polysaccharides, the number of live bacteria, their metabolic activity, the hydrophobicity of their surface, and the shape of their biofilms using laser confocal microscopy. Through transcriptome analysis, a total of 349 differentially expressed genes were identified, comprising 134 upregulated and 215 downregulated genes. GO functional enrichment analysis and KEGG pathway enrichment analysis revealed that oleanolic acid functions are through the regulation of bacterial motility, the iron absorption system, the two-component system, and adhesion pathways. These findings suggest that the main effects of oleanolic acid are to prevent bacterial motility, increase initial adhesion, and encourage the development of EcN biofilms. In addition, oleanolic acid interacts with iron absorption to cooperatively control the production of EcN biofilms within an optimal concentration range. Taking these results together, this study suggests that oleanolic acid may enhance probiotic biofilm formation in the intestines, presenting new avenues for probiotic product development.

Ferric Chloride Controls Citrus Anthracnose by Inducing the Autophagy Activity of Colletotrichum gloeosporioides

Colletotrichum gloeosporioides causes citrus anthracnose, which seriously endangers the pre-harvest production and post-harvest storage of citrus due to its devastating effects on fruit quality, shelf life, and profits. However, although some chemical agents have been proven to effectively control this plant disease, little to no efforts have been made to identify effective and safe anti-anthracnose alternatives. Therefore, this study assessed and verified the inhibitory effect of ferric chloride (FeCl₃) against C. gloeosporioides. Our findings demonstrated that FeCl₃ could effectively inhibit C. gloeosporioides spore germination. After FeCl₃ treatment, the germination rate of the spores in the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) groups decreased by 84.04% and 89.0%, respectively. Additionally, FeCl₃ could effectively inhibit the pathogenicity of C. gloeosporioides in vivo. Optical microscopy (OM) and scanning electron microscopy (SEM) analyses demonstrated the occurrence of wrinkled and atrophic mycelia. Moreover, FeCl₃ induced autophagosome formation in the test pathogen, as confirmed by transmission electron microscopy (TEM) and monodansylcadaverine (MDC) staining. Additionally, a positive correlation was identified between the FeCl₃ concentration and the damage rate of the fungal sporophyte cell membrane, as the staining rates of the control (untreated), 1/2 MIC, and MIC FeCl₃ treatment groups were 1.87%, 6.52%, and 18.15%, respectively. Furthermore, the ROS content in sporophyte cells increased by 3.6%, 29.27%, and 52.33% in the control, 1/2 MIC, and MIC FeCl₃ groups, respectively. Therefore, FeCl₃ could reduce the virulence and pathogenicity of C. gloeosporioides. Finally, FeCl₃-handled citrus fruit exhibited similar physiological qualities to water-handled fruit. The results show that FeCl₃ may prove to be a good substitute for the treatment of citrus anthracnose in the future.

In vitro effect of the iron chelator deferiprone on the antimicrobial susceptibility and biofilms of Burkholderia pseudomallei

This study evaluated the effect of the iron chelator deferiprone (DFP) on antimicrobial susceptibility and biofilm formation and maintenance by Burkholderia pseudomallei. Planktonic susceptibility to DFP alone and in combination with antibiotics was evaluated by broth microdilution and biofilm metabolic activity was determined with resazurin. DFP minimum inhibitory concentration (MIC) range was 4-64 µg/mL and in combination reduced the MIC for amoxicillin/clavulanate and meropenem. DFP reduced the biomass of biofilms by 21 and 12% at MIC and MIC/2, respectively. As for mature biofilms, DFP reduced the biomass by 47%, 59%, 52% and 30% at 512, 256, 128 and 64 µg/mL, respectively, but did not affect B. pseudomallei biofilm viability nor increased biofilm susceptibility to amoxicillin/clavulanate, meropenem and doxycycline. DFP inhibits planktonic growth and potentiates the effect of β-lactams against B. pseudomallei in the planktonic state and reduces biofilm formation and the biomass of B. pseudomallei biofilms.

Crosstalk between the Intestinal Virome and Other Components of the Microbiota, and Its Effect on Intestinal Mucosal Response and Diseases

In recent years, there has been ample evidence illustrating the effect of microbiota on gut immunity, homeostasis, and disease. Most of these studies have engaged more efforts in understanding the role of the bacteriome in gut mucosal immunity and disease. However, studies on the virome and its influence on gut mucosal immunity and pathology are still at infancy owing to limited metagenomic tools. Nonetheless, the existing studies on the virome have largely been focused on the bacteriophages as these represent the main component of the virome with little information on endogenous retroviruses (ERVs) and eukaryotic viruses. In this review, we describe the gut virome, and its role in gut mucosal response and disease progression. We also explore the crosstalk between the virome and other microorganisms in the gut mucosa and elaborate on how these interactions shape the gut mucosal immunity going from bacteriophages through ERVs to eukaryotic viruses. Finally, we elucidate the potential contribution of this crosstalk in the pathogenesis of inflammatory bowel diseases and colon cancer.

Effect of the combinatorial iron-chelation and oxidative stress on the growth of Aspergillus species

The growth of 14 Aspergillus strains belonging to nine species was studied under combinatorial deferriprone - H₂O₂ (iron-chelation - oxidative) stress. When deferriprone pretreated mycelia were subjected to even a weak oxidative stress, the growth inhibitory effect of iron-chelation stress was enhanced in 10 out of 14 strains. In contrast, oxidative stress pretreatment of conidia increased their deferriprone tolerance in 10 strains. Applying iron-chelators as antifungal agent or adjuvant can enhance the efficiency of the combinatorial iron withdrawal - oxidative stress strategy of our immune system and may reduce the survival of conidia escaped from the oxidative attack of pulmonary macrophages.

Metrics of Antifungal Effects of Ciprofloxacin on Aspergillus fumigatus Planktonic Growth and Biofilm Metabolism; Effects of Iron and Siderophores

Pseudomonas aeruginosa and Aspergillus fumigatus frequently coexist in the airways of immunocompromised patients or individuals with cystic fibrosis. Ciprofloxacin (CIP) is a synthetic quinolone antibiotic commonly used to treat bacterial infections, such as those produced by Pseudomonas aeruginosa. CIP binds iron, and it is unclear what effect this complex would have on the mycobiome. The effects of CIP on Aspergillus were dependent on the iron levels present, and on the presence of Aspergillus siderophores. We found that CIP alone stimulated wildtype planktonic growth, but not biofilm metabolism. At high concentrations, CIP antagonized a profungal effect of iron on wildtype Aspergillus metabolism, presumably owing to iron chelation. CIP interfered with the metabolism and growth of an Aspergillus siderophore mutant, with the effect on metabolism being antagonized by iron. CIP acted synergistically with iron on the growth of the mutant, and, to a lesser extent, the wildtype. In summary, CIP can increase fungal growth or affect fungal metabolism, depending on the local iron concentration and available siderophores. Therefore, high local CIP concentrations during treatment of Pseudomonas–Aspergillus co-infections may increase the fungal burden.

Virus Infection of Aspergillus fumigatus Compromises the Fungus in Intermicrobial Competition

Aspergillus and Pseudomonas compete in nature, and are the commonest bacterial and fungal pathogens in some clinical settings, such as the cystic fibrosis lung. Virus infections of fungi occur naturally. Effects on fungal physiology need delineation. A common reference Aspergillus fumigatus strain, long studied in two (of many) laboratories, was found infected with the AfuPmV-1 virus. One isolate was cured of virus, producing a virus-free strain. Virus from the infected strain was purified and used to re-infect three subcultures of the virus-free fungus, producing six fungal strains, otherwise isogenic. They were studied in intermicrobial competition with Pseudomonasaeruginosa. Pseudomonas culture filtrates inhibited forming or preformed Aspergillus biofilm from infected strains to a greater extent, also seen when Pseudomonas volatiles were assayed on Aspergillus. Purified iron-chelating Pseudomonas molecules, known inhibitors of Aspergillus biofilm, reproduced these differences. Iron, a stimulus of Aspergillus, enhanced the virus-free fungus, compared to infected. All infected fungal strains behaved similarly in assays. We show an important consequence of virus infection, a weakening in intermicrobial competition. Viral infection may affect the outcome of bacterial–fungal competition in nature and patients. We suggest that this occurs via alteration in fungal stress responses, the mechanism best delineated here is a result of virus-induced altered Aspergillus iron metabolism.

Influence of relevant cystic fibrosis bacteria on Scedosporium apiospermum and Scedosporium boydii growth and viability

Cystic fibrosis (CF) causes a variety of symptoms in different organs, but the majority of the morbidity and mortality of CF is related with pulmonary conditions. Primary infections are usually bacterial, and when treated with antibiotics, yeast infections appear or become more evident. Studies show that different microorganisms can co-inhabit the same environment and the interactions could be synergistic or antagonistic. Using techniques including viable and non-viable cell-to-cell interactions, mixed culture in liquid, and solid media sharing or not the supernatant, this study has evaluated interactions between the fungal species Scedosporium apiospermum and Scedosporium boydii with the bacterial species Staphylococcus aureus, Pseudomonas aeruginosa, and Burkholderia cepacia. Cell-to-cell interactions in liquid medium showed that P. aeruginosa and B. cepacia were able to reduce fungal viability but only in the presence of alive bacteria. Interactions without cell contact using a semi-permeable membrane showed that all bacteria were able to inhibit both fungal growths/viabilities. Cell-free supernatants from bacterial growth reduced fungal viability in planktonic fungal cells as well as in some conditions for preformed fungal biomass. According to the chemical analysis of the bacterial supernatants, the predominant component is protein. In this work, we verified that bacterial cells and their metabolites, present in the supernatants, can play anti-S. apiospermum and anti-S. boydii roles on fungal growth and viability.

Antifungal activity of deferiprone and EDTA against Sporothrix spp.: Effect on planktonic growth and biofilm formation

The present study evaluated the antifungal activity of the chelators deferiprone (DFP) and ethylenediaminetetraacetic acid (EDTA) and their effect on biofilm formation of the S. schenckii complex. Eighteen strains of Sporothrix spp. (seven S. brasiliensis, three S. globosa, three S. mexicana and five Sporothrix schenckii sensu stricto) were used. Minimum inhibitory concentration (MIC) values for EDTA and DFP against filamentous forms of Sporothrix spp. ranged from 32 to 128 μg/ml. For antifungal drugs, MIC values ranged from 0.25 to 4 μg/ml for amphotericin B, from 0.25 to 4 μg/ml for itraconazole, and from 0.03 to 0.25 μg/ml for terbinafine. The chelators caused inhibition of Sporothrix spp. in yeast form at concentrations ranging from 16 to 64 μg/ml (for EDTA) and 8 to 32 μg/ml (for DFP). For antifungal drugs, MIC values observed against the yeast varied from 0.03 to 0.5 μg/ml for AMB, 0.03 to 1 μg/ml for ITC, and 0.03 to 0.13 μg/ml for TRB. Both DFP and EDTA presented synergistic interaction with antifungals against Sporothrix spp. in both filamentous and yeast form. Biofilms formed in the presence of the chelators (512 μg/ml) showed a reduction of 47% in biomass and 45% in metabolic activity. Our data reveal that DFP and EDTA reduced the growth of planktonic cells of Sporothrix spp., had synergistic interaction with antifungal drugs against this pathogen, and reduced biofilm formation of Sporothrix spp.

LAY SUMMARY

Our data reveal that iron chelators deferiprone and ethylenediaminetetraacetic acid reduced the growth of planktonic cells of Sporothrix spp. as well as had synergistic interaction with antifungal drugs against this pathogen and reduced biofilm formation of Sporothrix spp.

The Application of Impedance Spectroscopy for Pseudomonas Biofilm Monitoring during Phage Infection

Bacterial biofilm prevention and eradication are common treatment problems, hence there is a need for advanced and precise experimental methods for its monitoring. Bacterial resistance to antibiotics has resulted in an interest in using a natural bacterial enemy-bacteriophages. In this study, we present the application of quartz tuning forks (QTF) as impedance sensors to determine in real-time the direct changes in Pseudomonas aeruginosa PAO1 biofilm growth dynamics during Pseudomonas phage LUZ 19 treatment at different multiplicities of infection (MOI). The impedance of the electric equivalent circuit (EEC) allowed us to measure the series resistance (Rs) corresponding to the growth-medium resistance (planktonic culture changes) and the conductance (G) corresponding to the level of QTF sensor surface coverage by bacterial cells and the extracellular polymer structure (EPS) matrix. It was shown that phage impacts on sessile cells (G dynamics) was very similar in the 10-day biofilm development regardless of applied MOI (0.1, 1 or 10). The application of phages at an early stage (at the sixth h) and on three-day biofilm caused a significant slowdown in biofilm dynamics, whereas the two-day biofilm turned out to be insensitive to phage infection. We observed an inhibitory effect of phage infection on the planktonic culture (Rs dynamics) regardless of the MOI applied and the time point of infection. Moreover, the Rs parameter made it possible to detect PAO1 population regrowth at the latest time points of incubation. The number of phage-insensitive forms reached the level of untreated culture at around the sixth day of infection. We conclude that the proposed impedance spectroscopy technique can be used to measure the physiological changes in the biofilm matrix composition, as well as the condition of planktonic cultures in order to evaluate the activity of anti-biofilm compounds.

N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine, a zinc chelator, inhibits biofilm and hyphal formation in Trichosporon asahii

Objective

Trichosporon asahii is the major causative fungus of disseminated or deep-seated trichosporonosis and forms a biofilm on medical devices. Biofilm formation leads to antifungal drug resistance, so biofilm-related infections are relatively difficult to treat and infected devices often require surgical removal. Therefore, prevention of biofilm formation is important in clinical settings. In this study, to identify metal cations that affect biofilm formation, we evaluated the effects of cation chelators on biofilm formation in T. asahii.

Results

We evaluated the effect of cation chelators on biofilm formation, since microorganisms must assimilate essential nutrients from their hosts to form and maintain biofilms. The inhibition by N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) was greater than those by other cation chelators, such as deferoxamine, triethylenetetramine, and ethylenediaminetetraacetic acid. The inhibitory effect of TPEN was suppressed by the addition of zinc. TPEN also inhibited T. asahii hyphal formation, which is related to biofilm formation, and the inhibition was suppressed by the addition of zinc. These results suggest that zinc is essential for biofilm formation and hyphal formation. Thus, zinc chelators have the potential to be developed into a new treatment for biofilm-related infection caused by T. asahii.

Novel intermicrobial molecular interaction: Pseudomonas aeruginosa Quinolone Signal (PQS) modulates Aspergillus fumigatus response to iron

Pseudomonas aeruginosa (Pa) and Aspergillus fumigatus (Af), the commonest bacterium and fungus in compromised host airways, compete for iron (Fe). The Pseudomonas quinolone signal (PQS), a Pa quorum sensing molecule, also chelates Fe, and delivers Fe to the Pa cell membrane using Pa siderophores. In models of Af biofilm formation or preformed biofilms, PQS inhibited Af in a low Fe environment. AfΔsidA (mutant unable to produce siderophores) biofilm was more sensitive to PQS inhibition than wild-type (WT), as was planktonic AfΔsidA growth. PQS decreased WT Af growth on agar. All these inhibitory actions were reversed by Fe. The Pa siderophore pyoverdin, or Af siderophore inhibitor celastrol, act cooperatively with PQS in Af inhibition. These findings all indicate PQS inhibition is owing to Fe chelation. Remarkably, in high Fe environments, PQS enhanced Af biofilm at 1/100 to 1/2000 Fe concentration required for Fe alone to enhance. Planktonic Af growth, and on agar, Af conidiation, were also enhanced by PQS+Fe compared to Fe alone. In contrast, neither AfΔsidA biofilm, nor planktonic AfΔsidA, were enhanced by PQS-Fe compared to Fe. When Af siderophore ferricrocin (FC),+PQS, were added to AfΔsidA, Af was then boosted more than by FC alone. Moreover, FC+PQS+Fe boosted AfΔsidA more than Fe, FC, FC+Fe, PQS+FC or PQS+Fe. Thus PQS-Fe maximal stimulation requires Af siderophores. PQS inhibits Af via chelation under low Fe conditions. In a high Fe environment, PQS paradoxically stimulates Af efficiently, and this involves Af siderophores. PQS production by Pa could stimulate Af in cystic fibrosis airways, where Fe homeostasis is altered and Fe levels increase, supporting fungal growth.

Iron: an essential nutrient for Aspergillus fumigatus and a fulcrum for pathogenesis

PURPOSE OF REVIEW

Aspergillus fumigatus is a ubiquitous saprophytic fungus that can cause life-threatening invasive aspergillosis in immunocompromised patients. Apart from the immune status of the host only a few characterized virulence factors have been identified. In this review, we describe the role of iron in the manifestation of A. fumigatus virulence.

RECENT FINDINGS

We gathered recent clinical evidence suggesting that tissue iron overload increases the risk of invasive aspergillosis occurrence. Furthermore, we summarize the mechanisms that A. fumigatus employs to achieve iron homeostasis and their importance in A. fumigatus proliferation in vitro. We describe two recent in-vivo models that clearly demonstrate the importance of iron in A. fumigatus growth and invasion.

SUMMARY

Based on these recent findings, therapy aimed at managing A. fumigatus iron homeostasis locally could make conditions more favorable to the host.

Intermicrobial interaction: Aspergillus fumigatus siderophores protect against competition by Pseudomonas aeruginosa

Pseudomonas aeruginosa and Aspergillus fumigatus are pathogens frequently co-inhabiting immunocompromised patient airways, particularly in people with cystic fibrosis. Both microbes depend on the availability of iron, and compete for iron in their microenvironment. We showed previously that the P. aeruginosa siderophore pyoverdine is the main instrument in battling A. fumigatus biofilms, by iron chelation and denial of iron to the fungus. Here we show that A. fumigatus siderophores defend against anti-fungal P. aeruginosa effects. P. aeruginosa supernatants produced in the presence of wildtype A. fumigatus planktonic supernatants (Afsup) showed less activity against A. fumigatus biofilms than P. aeruginosa supernatants without Afsup, despite higher production of pyoverdine by P. aeruginosa. Supernatants of A. fumigatus cultures lacking the sidA gene (AfΔsidA), unable to produce hydroxamate siderophores, were less capable of protecting A. fumigatus biofilms from P. aeruginosa supernatants and pyoverdine. AfΔsidA biofilm was more sensitive towards inhibitory effects of pyoverdine, the iron chelator deferiprone (DFP), or amphothericin B than wildtype A. fumigatus biofilm. Supplementation of sidA-deficient A. fumigatus biofilm with A. fumigatus siderophores restored resistance to pyoverdine. The A. fumigatus siderophore production inhibitor celastrol sensitized wildtype A. fumigatus biofilms towards the anti-fungal activity of DFP. In conclusion, A. fumigatus hydroxamate siderophores play a pivotal role in A. fumigatus competition for iron against P. aeruginosa.

Aspergillus-Pseudomonas interaction, relevant to competition in airways

In airways of immunocompromised patients and individuals with cystic fibrosis, Pseudomonas aeruginosa and Aspergillus fumigatus are the most common opportunistic bacterial and fungal pathogens. Both pathogens form biofilms and cause acute and chronic illnesses. Previous studies revealed that P. aeruginosa is able to inhibit A. fumigatus biofilms in vitro. While numerous P. aeruginosa molecules have been shown to affect A. fumigatus, there never has been a systematic approach to define the principal causative agent. We studied 24 P. aeruginosa mutants, with deletions in genes important for virulence, iron acquisition, or quorum sensing, for their ability to interfere with A. fumigatus biofilms. Cells, planktonic or biofilm culture filtrates of four P. aeruginosa mutants, pvdD-pchE-, pvdD-, lasR-rhlR-, and lasR-, inhibited A. fumigatus biofilm metabolism or planktonic A. fumigatus growth significantly less than P. aeruginosa wild type. The common defect of these four mutants was a lack in the production of the P. aeruginosa siderophore pyoverdine. Pure pyoverdine affected A. fumigatus biofilm metabolism, and restored inhibition by the above mutants. In lungs from cystic fibrosis patients, pyoverdine production and antifungal activity correlated. The key inhibitory mechanism for pyoverdine was iron-chelation and denial of iron to A. fumigatus. Further experiments revealed a counteracting, self-protective mechanism by A. fumigatus, based on A. fumigatus siderophore production.

Gene Expression Profiling of Bronchoalveolar Lavage Cells During Aspergillus Colonization of the Lung Allograft

BACKGROUND

Aspergillus colonization after lung transplant is associated with an increased risk of chronic lung allograft dysfunction (CLAD). We hypothesized that gene expression during Aspergillus colonization could provide clues to CLAD pathogenesis.

METHODS

We examined transcriptional profiles in 3- or 6-month surveillance bronchoalveolar lavage fluid cell pellets from recipients with Aspergillus fumigatus colonization (n = 12) and without colonization (n = 10). Among the Aspergillus colonized, we also explored profiles in those who developed CLAD (n = 6) or remained CLAD-free (n = 6). Transcription profiles were assayed with the HG-U133 Plus 2.0 microarray (Affymetrix). Differential gene expression was based on an absolute fold difference of 2.0 or greater and unadjusted P value less than 0.05. We used NIH Database for Annotation, Visualization and Integrated Discovery for functional analyses, with false discovery rates less than 5% considered significant.

RESULTS

Aspergillus colonization was associated with differential expression of 489 probe sets, representing 404 unique genes. "Defense response" genes and genes in the "cytokine-cytokine receptor" Kyoto Encyclopedia of Genes and Genomes pathway were notably enriched in this list. Among Aspergillus colonized patients, CLAD development was associated with differential expression of 69 probe sets, representing 64 unique genes. This list was enriched for genes involved in "immune response" and "response to wounding", among others. Notably, both chitinase 3-like-1 and chitotriosidase were associated with progression to CLAD.

CONCLUSIONS

Aspergillus colonization is associated with gene expression profiles related to defense responses including cytokine signaling. Epithelial wounding, as well as the innate immune response to chitin that is present in the fungal cell wall, may be key in the link between Aspergillus colonization and CLAD.

Perspectives of Phage Therapy in Non-bacterial Infections

While the true value of phage therapy (PT) in human bacterial infections still awaits formal confirmation by clinical trials, new data have been accumulating indicating that in the future PT may be applied in the treatment of non-bacterial infections. Thus, "phage guests" may interact with eukaryotic cells and such interactions with cells of the immune system may protect human health (Guglielmi, 2017) and cause clinically useful immunomodulatory and anti-inflammatory effects when administered for therapeutic purposes (Górski et al., 2017; Van Belleghem et al., 2017). Recently, a vision of how these effects could translate into advances in novel means of therapy in a variety of human pathologies secondary to immune disturbances and allergy was presented (Górski et al., 2018a). In this article we present what is currently known about anti-microbial effects of phage which are not directly related to their antibacterial action and how these findings could be applied in the future in treatment of viral and fungal infections.

Copper Influences the Antibacterial Outcomes of a β-Lactamase-Activated Prochelator against Drug-Resistant Bacteria

The unabated rise in bacterial resistance to conventional antibiotics, coupled with collateral damage to normal flora incurred by overuse of broad-spectrum antibiotics, necessitates the development of new antimicrobials targeted against pathogenic organisms. Here, we explore the antibacterial outcomes and mode of action of a prochelator that exploits the production of β-lactamase enzymes by drug-resistant bacteria to convert a nontoxic compound into a metal-binding antimicrobial agent directly within the microenvironment of pathogenic organisms. Compound PcephPT (phenylacetamido-cephem-pyrithione) contains a cephalosporin core linked to 2-mercaptopyridine N-oxide (pyrithione) via one of its metal-chelating atoms, which minimizes its preactivation interaction with metal ions and its cytotoxicity. Spectroscopic and chromatographic assays indicate that PcephPT releases pyrithione in the presence of β-lactamase-producing bacteria. The prochelator shows enhanced antibacterial activity against strains expressing β-lactamases, with bactericidal efficacy improved by the presence of low-micromolar copper in the growth medium. Metal analysis shows that cell-associated copper accumulation by the prochelator is significantly lower than that induced by pyrithione itself, suggesting that the location of pyrithione release influences biological outcomes. Low-micromolar (4-8 μg/mL) minimum inhibitory concentration (MIC) values of PcephPT in ceftriaxone-resistant bacteria compared with median lethal dose (LD50) values greater than 250 μM in mammalian cells suggests favorable selectivity. Further investigation into the mechanisms of prochelators will provide insight for the design of new antibacterial agents that manipulate cellular metallobiology as a strategy against infection.

Microhemorrhage-associated tissue iron enhances the risk for Aspergillus fumigatus invasion in a mouse model of airway transplantation

Invasive pulmonary disease due to the mold Aspergillus fumigatus can be life-threatening in lung transplant recipients, but the risk factors remain poorly understood. To study this process, we used a tracheal allograft mouse model that recapitulates large airway changes observed in patients undergoing lung transplantation. We report that microhemorrhage-related iron content may be a major determinant of A. fumigatus invasion and, consequently, its virulence. Invasive growth was increased during progressive alloimmune-mediated graft rejection associated with high concentrations of ferric iron in the graft. The role of iron in A. fumigatus invasive growth was further confirmed by showing that this invasive phenotype was increased in tracheal transplants from donor mice lacking the hemochromatosis gene (Hfe^-/- ). The invasive phenotype was also increased in mouse syngrafts treated with topical iron solution and in allograft recipients receiving deferoxamine, a chelator that increases iron bioavailability to the mold. The invasive growth of the iron-intolerant A. fumigatus double-knockout mutant (ΔsreA/ΔcccA) was lower than that of the wild-type mold. Alloimmune-mediated microvascular damage and iron overload did not appear to impair the host's immune response. In human lung transplant recipients, positive staining for iron in lung transplant tissue was more commonly seen in endobronchial biopsy sections from transplanted airways than in biopsies from the patients' own airways. Collectively, these data identify iron as a major determinant of A. fumigatus invasive growth and a potential target to treat or prevent A. fumigatus infections in lung transplant patients.

Studies of Pseudomonas aeruginosa Mutants Indicate Pyoverdine as the Central Factor in Inhibition of Aspergillus fumigatus Biofilm

Pseudomonas aeruginosa and Aspergillus fumigatus are common opportunistic bacterial and fungal pathogens, respectively. They often coexist in airways of immunocompromised patients and individuals with cystic fibrosis, where they form biofilms and cause acute and chronic illnesses. Hence, the interactions between them have long been of interest and it is known that P. aeruginosa can inhibit A. fumigatusin vitro We have approached the definition of the inhibitory P. aeruginosa molecules by studying 24 P. aeruginosa mutants with various virulence genes deleted for the ability to inhibit A. fumigatus biofilms. The ability of P. aeruginosa cells or their extracellular products produced during planktonic or biofilm growth to affect A. fumigatus biofilm metabolism or planktonic A. fumigatus growth was studied in agar and liquid assays using conidia or hyphae. Four mutants, the pvdD pchE, pvdD, lasR rhlR, and lasR mutants, were shown to be defective in various assays. This suggested the P. aeruginosa siderophore pyoverdine as the key inhibitory molecule, although additional quorum sensing-regulated factors likely contribute to the deficiency of the latter two mutants. Studies of pure pyoverdine substantiated these conclusions and included the restoration of inhibition by the pyoverdine deletion mutants. A correlation between the concentration of pyoverdine produced and antifungal activity was also observed in clinical P. aeruginosa isolates derived from lungs of cystic fibrosis patients. The key inhibitory mechanism of pyoverdine was chelation of iron and denial of iron to A. fumigatusIMPORTANCE Interactions between human pathogens found in the same body locale are of vast interest. These interactions could result in exacerbation or amelioration of diseases. The bacterium Pseudomonas aeruginosa affects the growth of the fungus Aspergillus fumigatus Both pathogens form biofilms that are resistant to therapeutic drugs and host immunity. P. aeruginosa and A. fumigatus biofilms are found in vivo, e.g., in the lungs of cystic fibrosis patients. Studying 24 P. aeruginosa mutants, we identified pyoverdine as the major anti-A. fumigatus compound produced by P. aeruginosa Pyoverdine captures iron from the environment, thus depriving A. fumigatus of a nutrient essential for its growth and metabolism. We show how microbes of different kingdoms compete for essential resources. Iron deprivation could be a therapeutic approach to the control of pathogen growth.

Iron acquisition in fungal pathogens of humans

The devastating infections that fungal pathogens cause in humans are underappreciated relative to viral, bacterial and parasitic diseases. In recent years, the contributions to virulence of reductive iron uptake, siderophore-mediated uptake and heme acquisition have been identified in the best studied and most life-threatening fungal pathogens: Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus. In particular, exciting new work illustrates the importance of iron acquisition from heme and hemoglobin in the virulence of pathogenic yeasts. However, the challenge of establishing how these fungi gain access to hemoglobin in blood and to other sources of heme remains to be fully addressed. Recent studies are also expanding our knowledge of iron uptake in less-well studied fungal pathogens, including dimorphic fungi where new information reveals an integration of iron acquisition with morphogenesis and cell-surface properties for adhesion to host cells. Overall, the accumulating information provides opportunities to exploit iron acquisition for antifungal therapy, and new work highlights the development of specific inhibitors of siderophore biosynthesis and metal chelators for therapeutic use alone or in conjunction with existing antifungal drugs. It is clear that iron-related therapies will need to be customized for specific diseases because the emerging view is that fungal pathogens use different combinations of strategies for iron acquisition in the varied niches of vertebrate hosts.

Pseudomonas phage inhibition of Candida albicans

Pseudomonas aeruginosa (Pa) and Candida albicans (Ca) are major bacterial and fungal pathogens in immunocompromised hosts, and notably in the airways of cystic fibrosis patients. The bacteriophages of Pa physically alter biofilms, and were recently shown to inhibit the biofilms of Aspergillus fumigatus. To understand the range of this viral-fungal interaction, we studied Pa phages Pf4 and Pf1, and their interactions with Ca biofilm formation and preformed Ca biofilm. Both forms of Ca biofilm development, as well as planktonic Ca growth, were inhibited by either phage. The inhibition of biofilm was reversed by the addition of iron, suggesting that the mechanism of phage action on Ca involves denial of iron. Birefringence studies on added phage showed an ordered structure of binding to Ca. Electron microscopic observations indicated phage aggregation in the biofilm extracellular matrix. Bacteriophage-fungal interactions may be a general feature with several pathogens in the fungal kingdom.

Verapamil Inhibits Aspergillus Biofilm, but Antagonizes Voriconazole

The paucity of effective antifungals against Aspergillus and increasing resistance, the recognition of the importance of Aspergillus biofilm in several clinical settings, and reports of verapamil—a calcium channel blocker—efficacy against Candida biofilm and hyphal growth, and synergy with an azole antifungal in vitro, led to a study of verapamil ± voriconazole against Aspergillus. Broth macrodilution methodology was utilized for MIC (minimum inhibitory concentration) and MFC (minimum fungicidal concentration) determination. The metabolic effects (assessed by XTT [2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide inner salt]) on biofilm formation by conidia were studied upon exposure to verapamil, verapamil plus voriconazole, or voriconazole alone. For biofilm formation, we found less inhibition from the combinations than with either drug alone, or less inhibition from the combination than that of the more potent drug alone. For preformed biofilm, we found no significant change in activity comparing voriconazole alone compared to added verapamil, and no significant alteration of activity of the more potent voriconazole, at any concentration in the range tested, by addition of a concentration of verapamil that is inhibitory alone. In full checkerboard assays with planktonic fungus, there was no indication of any effect of one drug on the other (indifference). Although verapamil was similarly inactive against planktonic Aspergillus, as with Candida, verapamil was indeed active against Aspergillus biofilm. However, indifference and antagonism was found with voriconazole.

Effect of acute predation with bacteriophage on intermicrobial aggression by Pseudomonas aeruginosa

In persons with structural lung disease, particularly those with cystic fibrosis (CF), chronic airway infections cause progressive loss of lung function. CF airways can be colonized by a variety of microorganisms; the most frequently encountered bacterial and fungal pathogens are Pseudomonas aeruginosa and Aspergillus fumigatus, respectively. Co-infection with P. aeruginosa and A. fumigatus often results in a more rapid loss of lung function, indicating that interactions between these pathogens affect infection pathogenesis. There has been renewed interest in the use of viruses (bacteriophage, mycoviruses) as alternatives to antibiotics to treat these infections. In previous work, we found that filamentous Pf bacteriophage produced by P. aeruginosa directly inhibited the metabolic activity of A. fumigatus by binding to and sequestering iron. In the current study, we further examined how filamentous Pf bacteriophage affected interactions between P. aeruginosa and A. fumigatus. Here, we report that the antifungal properties of supernatants collected from P. aeruginosa cultures infected with Pf bacteriophage were substantially less inhibitory towards A. fumigatus biofilms. In particular, we found that acute infection of P. aeruginosa by Pf bacteriophage inhibited the production of the virulence factor pyoverdine. Our results raise the possibility that the reduced production of antimicrobials by P. aeruginosa infected by Pf bacteriophage may promote conditions in CF airways that allow co-infection with A. fumigatus to occur, exacerbating disease severity. Our results also highlight the importance of considering how the use of bacteriophage as therapeutic agents could affect the behavior and composition of polymicrobial communities colonizing sites of chronic infection.

Effect of Anaerobiasis or Hypoxia on Pseudomonas aeruginosa Inhibition of Aspergillus fumigatus Biofilm

Pseudomonas aeruginosa (Pa) and Aspergillus fumigatus (Af) are the major bacterial and fungal pathogens in the airways of cystic fibrosis (CF) patients. This is likely related to their ability to form biofilms. Both microbes have been associated with CF disease progression. The interplay between these two pathogens has been studied under aerobic conditions, though accumulating data indicates that much of the CF airway is hypoxic or anaerobic. We studied the microbial interaction in these latter environments. Pa is an aggressor against Af forming biofilm or as established Af biofilm, whether Pa is cultivated in aerobic, hypoxic, or anaerobic conditions, or tested in aerobic or hypoxic conditions. Pa cells are generally more effective than planktonic or biofilm culture filtrates. Pa growth is less in anaerobic conditions, and filtrates less effective after anaerobic or hypoxic growth, or against hypoxic Af. These, and other comparisons shown, indicate that Pa would be less effective in such environments, as would be the case in a CF mucus plug. These observations would explain why Pa becomes established in CF airways before Af, and why Af may persist during disease progression.

Are Cystic Fibrosis Aspergillus fumigatus Isolates Different? Intermicrobial Interactions with Pseudomonas

Pseudomonas aeruginosa and Aspergillus fumigatus are the leading bacterial and fungal pathogens in cystic fibrosis (CF). We have shown that Af biofilms are susceptible to Pseudomonas, particularly CF phenotypes. Those studies were performed with a reference virulent non-CF Aspergillus. Pseudomonas resident in CF airways undergo profound genetic and phenotypic adaptations to the abnormal environment. Studies have also indicated Aspergillus from CF patients have unexpected profiles of antifungal susceptibility. This would suggest that Aspergillus isolates from CF patients may be different or altered from other clinical isolates. It is important to know whether Aspergillus may also be altered, as a result of that CF environment, in susceptibility to Pseudomonas. CF Aspergillus proved not different in that susceptibility.

Pf4 bacteriophage produced by Pseudomonas aeruginosa inhibits Aspergillus fumigatus metabolism via iron sequestration

Pseudomonas aeruginosa (Pa) and Aspergillus fumigatus (Af) are major human pathogens known to interact in a variety of disease settings, including airway infections in cystic fibrosis. We recently reported that clinical CF isolates of Pa inhibit the formation and growth of Af biofilms. Here, we report that the bacteriophage Pf4, produced by Pa, can inhibit the metabolic activity of Af biofilms. This phage-mediated inhibition was dose dependent, ablated by phage denaturation, and was more pronounced against preformed Af biofilm rather than biofilm formation. In contrast, planktonic conidial growth was unaffected. Two other phages, Pf1 and fd, did not inhibit Af, nor did supernatant from a Pa strain incapable of producing Pf4. Pf4, but not Pf1, attaches to Af hyphae in an avid and prolonged manner, suggesting that Pf4-mediated inhibition of Af may occur at the biofilm surface. We show that Pf4 binds iron, thus denying Af a crucial resource. Consistent with this, the inhibition of Af metabolism by Pf4 could be overcome with supplemental ferric iron, with preformed biofilm more resistant to reversal. To our knowledge, this is the first report of a bacterium producing a phage that inhibits the growth of a fungus and the first description of a phage behaving as an iron chelator in a biological system.

Biofilm Filtrates of Pseudomonas aeruginosa Strains Isolated from Cystic Fibrosis Patients Inhibit Preformed Aspergillus fumigatus Biofilms via Apoptosis

Pseudomonas aeruginosa (Pa) and Aspergillus fumigatus (Af) colonize cystic fibrosis (CF) patient airways. Pa culture filtrates inhibit Af biofilms, and Pa non-CF, mucoid (Muc-CF) and nonmucoid CF (NMuc-CF) isolates form an ascending inhibitory hierarchy. We hypothesized this activity is mediated through apoptosis induction. One Af and three Pa (non-CF, Muc-CF, NMuc-CF) reference isolates were studied. Af biofilm was formed in 96 well plates for 16 h ± Pa biofilm filtrates. After 24 h, apoptosis was characterized by viability dye DiBAc, reactive oxygen species (ROS) generation, mitochondrial membrane depolarization, DNA fragmentation and metacaspase activity. Muc-CF and NMuc-CF filtrates inhibited and damaged Af biofilm (p<0.0001). Intracellular ROS levels were elevated (p<0.001) in NMuc-CF-treated Af biofilms (3.7- fold) compared to treatment with filtrates from Muc-CF- (2.5- fold) or non-CF Pa (1.7- fold). Depolarization of mitochondrial potential was greater upon exposure to NMuc-CF (2.4-fold) compared to Muc-CF (1.8-fold) or non-CF (1.25-fold) (p<0.0001) filtrates. Exposure to filtrates resulted in more DNA fragmentation in Af biofilm, compared to control, mediated by metacaspase activation. In conclusion, filtrates from CF-Pa isolates were more inhibitory against Af biofilms than from non-CF. The apoptotic effect involves mitochondrial membrane damage associated with metacaspase activation.