Inactivation of the antifungal and immunomodulatory properties of human cathelicidin LL-37 by aspartic proteases produced by the pathogenic yeast Candida albicans

Secreted Aspartic Proteinases: Key Factors in Candida Infections and Host-Pathogen Interactions

Extracellular proteases are key factors contributing to the virulence of pathogenic fungi from the genus Candida. Their proteolytic activities are crucial for extracting nutrients from the external environment, degrading host defenses, and destabilizing the internal balance of the human organism. Currently, the enzymes most frequently described in this context are secreted aspartic proteases (Saps). This review comprehensively explores the multifaceted roles of Saps, highlighting their importance in biofilm formation, tissue invasion through the degradation of extracellular matrix proteins and components of the coagulation cascade, modulation of host immune responses via impairment of neutrophil and monocyte/macrophage functions, and their contribution to antifungal resistance. Additionally, the diagnostic challenges associated with Candida infections and the potential of Saps as biomarkers were discussed. Furthermore, we examined the prospects of developing vaccines based on Saps and the use of protease inhibitors as adjunctive therapies for candidiasis. Given the complex biology of Saps and their central role in Candida pathogenicity, a multidisciplinary approach may pave the way for innovative diagnostic strategies and open new opportunities for innovative clinical interventions against candidiasis.

Cathelicidin boosts the antifungal activity of neutrophils and improves prognosis during Aspergillus fumigatus keratitis

Aspergillus fumigatus (A. fumigatus) is one of the common pathogens of fungal keratitis. Fungal growth and invasion cause excessive inflammation and corneal damage, leading to severe vision loss. Neutrophils are the primary infiltrating cells critical for fungal clearance. Cathelicidin [LL-37 in humans and cathelicidin-related antimicrobial peptide (CRAMP) in mice], a natural antimicrobial peptide, can directly inhibit the growth of many pathogens and regulate immune responses. However, the role of cathelicidin and its effect on neutrophils in A. fumigatus keratitis remain unclear. By establishing A. fumigatus keratitis mouse models, we found that cathelicidin was increased in A. fumigatus keratitis. It could reduce fungal loads, lower clinical scores, and improve corneal transparency. Restriction of CRAMP on fungal proliferation was largely counteracted in CD18-/- mice, in which neutrophils cannot migrate into infected sites. When WT neutrophils were transferred into CD18-/- mice, corneal fungal loads were distinctly reduced, indicating that neutrophils are vital for CRAMP-mediated resistance. Furthermore, cathelicidin promoted neutrophils to phagocytose and degrade conidia both in vitro and in vivo. CXC chemokine receptor 2 (CXCR2) was reported to be a functional receptor of LL-37 on neutrophils. CXCR2 antagonist SB225002 or phospholipase C (PLC) inhibitor U73122 weakened LL-37-induced phagocytosis. Meanwhile, LL-37 induced PLC γ phosphorylation, which was attenuated by SB225002. SB225002 or the autophagy inhibitors Bafilomycin-A1 and 3-Methyladenine weakened LL-37-induced degradation of conidia. Transmission electron microscopy (TEM) observed that LL-37 increased autophagosomes in Aspergillus-infected neutrophils. Consistently, LL-37 elevated autophagy-associated protein expressions (Beclin-1 and LC3-II), but this effect was weakened by SB225002. Collectively, cathelicidin reduces fungal loads and improves the prognosis of A. fumigatus keratitis. Both in vitro and in vivo, cathelicidin promotes neutrophils to phagocytose and degrade conidia. LL-37/CXCR2 activates PLC γ to amplify neutrophils' phagocytosis and induces autophagy to eliminate intracellular conidia.

Complexation of fungal extracellular nucleic acids by host LL-37 peptide shapes neutrophil response to Candida albicans biofilm

Candida albicans remains the predominant cause of fungal infections, where adhered microbial cells form biofilms - densely packed communities. The central feature of C. albicans biofilms is the production of an extracellular matrix (ECM) consisting of polymers and extracellular nucleic acids (eDNA, eRNA), which significantly impedes the infiltration of host cells. Neutrophils, as crucial players in the innate host defense, employ several mechanisms to eradicate the fungal infection, including NETosis, endocytosis, or the release of granules containing, among others, antimicrobial peptides (AMPs). The main representative of these is the positively charged peptide LL-37 formed from an inactive precursor (hCAP18). In addition to its antimicrobial functions, this peptide possesses a propensity to interact with negatively charged molecules, including nucleic acids. Our in vitro studies have demonstrated that LL-37 contacting with C. albicans nucleic acids, isolated from biofilm, are complexed by the peptide and its shorter derivatives, as confirmed by electrophoretic mobility shift assays. We indicated that the generation of the complexes induces discernible alterations in the neutrophil response to fungal nucleic acids compared to the effects of unconjugated molecules. Our analyses involving fluorescence microscopy, flow cytometry, and Western blotting revealed that stimulation of neutrophils with DNA:LL-37 or RNA:LL-37 complexes hamper the activation of pro-apoptotic caspases 3 and 7 and fosters increased activation of anti-apoptotic pathways mediated by the Mcl-1 protein. Furthermore, the formation of complexes elicits a dual effect on neutrophil immune response. Firstly, they facilitate increased nucleic acid uptake, as evidenced by microscopic observations, and enhance the pro-inflammatory response, promoting IL-8 production. Secondly, the complexes detection suppresses the production of reactive oxygen species and attenuates NETosis activation. In conclusion, these findings may imply that the neutrophil immune response shifts toward mobilizing the immune system as a whole, rather than inactivating the pathogen locally. Our findings shed new light on the intricate interplay between the constituents of the C. albicans biofilm and the host's immune response and indicate possible reasons for the elimination of NETosis from the arsenal of the neutrophil response during contact with the fungal biofilm.

Efficacy of Ceragenins in Controlling the Growth of Oral Microorganisms: Implications for Oral Hygiene Management

Ensuring proper dental hygiene is of paramount importance for individuals' general well-being, particularly for patients receiving medical care. There is a prevailing utilization of conventional oral hygiene items, including toothbrushes and mouthwashes, which have gained widespread acceptance; nevertheless, their limitations encourage investigating novel options in this domain. Our study indicates that ceragenins (CSAs) being lipid analogs of host defense peptides, well-recognized for their wide-ranging antimicrobial properties, may be a potentially efficacious means to augment oral hygiene in hospitalized individuals. We demonstrate that ceragenins CSA-13, CSA-44, and CSA-131 as well as undescribed to date CSA-255 display potent antimicrobial activities against isolates of fungi, aerobic, and anaerobic bacteria from Candida, Streptococcus, Enterococcus, and Bacteroides species, which are well-recognized representatives of microbes found in the oral cavity. These effects were further confirmed against mono- and dual-species fungal and bacterial biofilms. While the ceragenins showed similar or slightly diminished efficacy compared to commercially available mouthwashes, they demonstrated a highly favorable toxicity profile toward host cells, that may translate into better maintenance of host mucosal membrane stability. This suggests that incorporating ceragenins into oral hygiene products could be a valuable strategy for reducing the risk of both oral cavity-localized and secondary systemic infections and for improving the overall health outcomes of individuals receiving medical treatment.

Candida albicans Biofilm-Derived Extracellular Vesicles Are Involved in the Tolerance to Caspofungin, Biofilm Detachment, and Fungal Proteolytic Activity

It has been repeatedly reported that the cells of organisms in all kingdoms of life produce nanometer-sized lipid membrane-enveloped extracellular vesicles (EVs), transporting and protecting various substances of cellular origin. While the composition of EVs produced by human pathogenic fungi has been studied in recent decades, another important challenge is the analysis of their functionality. Thus far, fungal EVs have been shown to play significant roles in intercellular communication, biofilm production, and modulation of host immune cell responses. In this study, we verified the involvement of biofilm-derived EVs produced by two different strains of Candida albicans-C. albicans SC5314 and 3147 (ATCC 10231)-in various aspects of biofilm function by examining its thickness, stability, metabolic activity, and cell viability in the presence of EVs and the antifungal drug caspofungin. Furthermore, the proteolytic activity against the kininogen-derived antimicrobial peptide NAT26 was confirmed by HPLC analysis for C. albicans EVs that are known to carry, among others, particular members of the secreted aspartic proteinases (Saps) family. In conclusion, EVs derived from C. albicans biofilms were shown to be involved in biofilm tolerance to caspofungin, biofilm detachment, and fungal proteolytic activity.

A heptadeca amino acid peptide subunit of cathelicidin LL-37 has previously unreported antifungal activity

Yeasts such as Candida albicans, albeit being ubiquitous members of the skin, oral and vaginal microbiome, can cause superficial to life-threatening infections. Human cathelicidin LL-37-based peptides have antibacterial activity and yet, their antifungal activity remains to be thoroughly characterized. The aim of this study was to comprehensively investigate the activity of LL-37-based peptides against C. albicans. LL-37 and its derivatives were tested for their ability to kill C. albicans planktonic cells in the presence of various biological matrices (serum, plasma, saliva and urine), that have been reported to inactivate peptides. The antibiofilm activity, resistance development and biocompatibility were investigated for the lead peptide. GK-17, a 17 amino acid peptide, showed remarkable stability to fungal aspartyl proteases and rapidly killed planktonic C. albicans despite the presence of biological matrices. GK-17 also inhibited adhesion to biotic and abiotic substrates, inhibited biofilm formation and eradicated preformed biofilms in the presence of biological matrices. Compared to nystatin, GK-17 had a lower propensity to allow for resistance development by C. albicans. The peptide showed concentration-dependent biocompatibility to red blood cells, with only 30% hemolysis even at 4× the fungicidal concentration. Taken together, GK-17 is a novel antifungal peptide with promising effects against C. albicans.

Living together: The role of Candida albicans in the formation of polymicrobial biofilms in the oral cavity

The oral cavity of humans is colonized by diversity of microbial community, although dominated by bacteria, it is also constituted by a low number of fungi, often represented by Candida albicans. Although in the vast minority, this usually commensal fungus under certain conditions of the host (e.g., immunosuppression or antibiotic therapy), can transform into an invasive pathogen that adheres to mucous membranes and also to medical or dental devices, causing mucosal infections. This transformation is correlated with changes in cell morphology from yeast-like cells to hyphae and is supported by numerous virulence factors exposed by C. albicans cells at the site of infection, such as multifunctional adhesins, degradative enzymes, or toxin. All of them affect the surrounding host cells or proteins, leading to their destruction. However, at the site of infection, C. albicans can interact with different bacterial species and in its filamentous form may produce biofilms-the elaborated consortia of microorganisms, that present increased ability to host colonization and resistance to antimicrobial agents. In this review, we highlight the modification of the infectious potential of C. albicans in contact with different bacterial species, and also consider the mutual bacterial-fungal relationships, involving cooperation, competition, or antagonism, that lead to an increase in the propagation of oral infection. The mycofilm of C. albicans is an excellent hiding place for bacteria, especially those that prefer low oxygen availability, where microbial cells during mutual co-existence can avoid host recognition or elimination by antimicrobial action. However, these microbial relationships, identified mainly in in vitro studies, are modified depending on the complexity of host conditions and microbial dominance in vivo.

Peptide Stability Is Important but Not a General Requirement for Antimicrobial and Antibiofilm Activity In Vitro and In Vivo

Peptide stability to proteases has been a major requirement for developing peptide therapeutics. This study investigates the effects of peptide stability on antimicrobial and antibiofilm activity under various conditions. For this purpose, two human cathelicidin-derived peptides differing in stability to proteases were utilized. While GF-17, a peptide derived from the major antimicrobial region of human LL-37, can be rapidly cleaved by proteases, the engineered peptide 17BIPHE2 is resistant to multiple proteases. In the standard antimicrobial susceptibility, killing kinetics, and membrane permeabilization assays conducted in vitro using planktonic bacteria, these two peptides displayed similar potency. The two peptides were also similarly active against methicillin-resistant Staphylococcus aureus (MRSA) USA300 prior to biofilm formation. However, 17BIPHE2 was superior to GF-17 in disrupting preformed biofilms probably due to both enhanced stability and slightly higher DNA binding capacity. In a wax moth model, 17BIPHE2 better protected insects from MRSA infection-caused death than GF-17, consistent with the slower degradation of 17BIPHE2 than GF-17. Here, peptide antimicrobial activity was found to be critical for in vivo efficacy. When incorporated in the nanofiber/microneedle delivery device, GF-17 and 17BIPHE2 displayed a similar effect in eliminating MRSA in murine chronic wounds, underscoring the advantage of nanofibers in protecting the peptide from degradation. Since nanoformulation can ease the requirement of peptide stability, it opens the door to a direct use of natural peptides or their cocktails for antimicrobial treatment, accelerating the search of effective antibiofilm peptides to treat chronic wounds.

Antimicrobial Peptides with Anti-Candida Activity

Mycoses are accountable for millions of infections yearly worldwide. Invasive candidiasis is the most usual, presenting a high morbidity and mortality. Candida albicans remains the prevalent etiologic agent, but the incidence of other species such as Candida parapsilosis, Candida glabrata and Candida auris keeps increasing. These pathogens frequently show a reduced susceptibility to commonly used antifungal drugs, including polyenes, triazoles and echinocandins, and the incidence of emerging multi-drug-resistant strains of these species continues to increase. Therefore, the need to search for new molecules that target these pathogenic species in a different manner is now more urgent than ever. Nature is an almost endless source of interesting new molecules that could meet this need. Among these molecules, antimicrobial peptides, present in different sources in nature, possess some advantages over conventional antifungal agents, even with their own drawbacks, and are considered as a promising pharmacological option against a wide range of microbial infections. In this review, we describe 20 antimicrobial peptides from different origins that possess an activity against Candida.

The emerging role of neutrophil extracellular traps in fungal infection

Fungal infections are global public health problems and can lead to substantial human morbidity and mortality. Current antifungal therapy is not satisfactory, especially for invasive, life-threatening fungal infections. Modulating the antifungal capacity of the host immune system is a feasible way to combat fungal infections. Neutrophils are key components of the innate immune system that resist fungal pathogens by releasing reticular extracellular structures called neutrophil extracellular traps (NETs). When compared with phagocytosis and oxidative burst, NETs show better capability in terms of trapping large pathogens, such as fungi. This review will summarize interactions between fungal pathogens and NETs. Molecular mechanisms of fungi-induced NETs formation and defensive strategies used by fungi are also discussed.

Proteinous Components of Neutrophil Extracellular Traps Are Arrested by the Cell Wall Proteins of Candida albicans during Fungal Infection, and Can Be Used in the Host Invasion

One of defense mechanisms of the human immune system to counteract infection by the opportunistic fungal pathogen Candida albicans is the recruitment of neutrophils to the site of invasion, and the subsequent production of neutrophil extracellular traps (NETs) that efficiently capture and kill the invader cells. In the current study, we demonstrate that within these structures composed of chromatin and proteins, the latter play a pivotal role in the entrapment of the fungal pathogen. The proteinous components of NETs, such as the granular enzymes elastase, myeloperoxidase and lactotransferrin, as well as histones and cathelicidin-derived peptide LL-37, are involved in contact with the surface of C. albicans cells. The fungal partners in these interactions are a typical adhesin of the agglutinin-like sequence protein family Als3, and several atypical surface-exposed proteins of cytoplasmic origin, including enolase, triosephosphate isomerase and phosphoglycerate mutase. Importantly, the adhesion of both the elastase itself and the mixture of proteins originating from NETs on the C. albicans cell surface considerably increased the pathogen potency of human epithelial cell destruction compared with fungal cells without human proteins attached. Such an implementation of adsorbed NET-derived proteins by invading C. albicans cells might alter the effectiveness of the fungal pathogen entrapment and affect the further host colonization.

Secretory Proteases of the Human Skin Microbiome

The human skin is our outermost layer and serves as a protective barrier against external insults. Advances in next generation sequencing have enabled the discoveries of a rich and diverse community of microbes - bacteria, fungi and viruses that are residents of this surface. The genomes of these microbes also revealed the presence of many secretory enzymes. In particular, proteases which are hydrolytic enzymes capable of protein cleavage and degradation are of special interest in the skin environment which is enriched in proteins and lipids. In this minireview, we will focus on the roles of these skin-relevant microbial secreted proteases, both in terms of their widely studied roles as pathogenic agents in tissue invasion and host immune inactivation, and their recently discovered roles in inter-microbial interactions and modulation of virulence factors. From these studies, it has become apparent that while microbial proteases are capable of a wide range of functions, their expression is tightly regulated and highly responsive to the environments the microbes are in. With the introduction of new biochemical and bioinformatics tools to study protease functions, it will be important to understand the roles played by skin microbial secretory proteases in cutaneous health, especially the less studied commensal microbes with an emphasis on contextual relevance.

Fungal immunity and pathogenesis in mammals versus the invertebrate model organism Galleria mellonella

In recent decades, Galleria mellonella (Lepidoptera: Pyralidae) have emerged as a model system to explore experimental aspects of fungal pathogenesis. The benefits of the G. mellonella model include being faster, cheaper, higher throughput and easier compared with vertebrate models. Additionally, as invertebrates, their use is subject to fewer ethical and regulatory issues. However, for G. mellonella models to provide meaningful insight into fungal pathogenesis, the G. mellonella-fungal interactions must be comparable to mammalian-fungal interactions. Indeed, as discussed in the review, studies suggest that G. mellonella and mammalian immune systems share many similarities, and fungal virulence factors show conserved functions in both hosts. While the moth model has opened novel research areas, many comparisons are superficial and leave large gaps of knowledge that need to be addressed concerning specific mechanisms underlying G. mellonella-fungal interactions. Closing these gaps in understanding will strengthen G. mellonella as a model for fungal virulence in the upcoming years. In this review, we provide comprehensive comparisons between fungal pathogenesis in mammals and G. mellonella from immunological and virulence perspectives. When information on an antifungal immune component is unknown in G. mellonella, we include findings from other well-studied Lepidoptera. We hope that by outlining this information available in related species, we highlight areas of needed research and provide a framework for understanding G. mellonella immunity and fungal interactions.

An Opaque Cell-Specific Expression Program of Secreted Proteases and Transporters Allows Cell-Type Cooperation in Candida albicans

An unusual feature of the opportunistic pathogen Candida albicans is its ability to switch stochastically between two distinct, heritable cell types called white and opaque. Here, we show that only opaque cells, in response to environmental signals, massively upregulate a specific group of secreted proteases and peptide transporters, allowing exceptionally efficient use of proteins as sources of nitrogen. We identify the specific proteases [members of the secreted aspartyl protease (SAP) family] needed for opaque cells to proliferate under these conditions, and we identify four transcriptional regulators of this specialized proteolysis and uptake program. We also show that, in mixed cultures, opaque cells enable white cells to also proliferate efficiently when proteins are the sole nitrogen source. Based on these observations, we suggest that one role of white-opaque switching is to create mixed populations where the different phenotypes derived from a single genome are shared between two distinct cell types.

Innate Inspiration: Antifungal Peptides and Other Immunotherapeutics From the Host Immune Response

The purpose of this review is to describe antifungal therapeutic candidates in preclinical and clinical development derived from, or directly influenced by, the immune system, with a specific focus on antimicrobial peptides (AMP). Although the focus of this review is AMP with direct antimicrobial effects on fungi, we will also discuss compounds with direct antifungal activity, including monoclonal antibodies (mAb), as well as immunomodulatory molecules that can enhance the immune response to fungal infection, including immunomodulatory AMP, vaccines, checkpoint inhibitors, interferon and colony stimulating factors as well as immune cell therapies. The focus of this manuscript will be a non-exhaustive review of antifungal compounds in preclinical and clinical development that are based on the principles of immunology and the authors acknowledge the incredible amount of in vitro and in vivo work that has been conducted to develop such therapeutic candidates.

Plant-Derived Substances in the Fight Against Infections Caused by Candida Species

Yeast-like fungi from the Candida genus are predominantly harmless commensals that colonize human skin and mucosal surfaces, but under conditions of impaired host immune system change into dangerous pathogens. The pathogenicity of these fungi is typically accompanied by increased adhesion and formation of complex biofilms, making candidal infections challenging to treat. Although a variety of antifungal drugs have been developed that preferably attack the fungal cell wall and plasma membrane, these pathogens have acquired novel defense mechanisms that make them resistant to standard treatment. This causes an increase in the incidence of candidiasis and enforces the urgent need for an intensified search for new specifics that could be helpful, alone or synergistically with traditional drugs, for controlling Candida pathogenicity. Currently, numerous reports have indicated the effectiveness of plant metabolites as potent antifungal agents. These substances have been shown to inhibit growth and to alter the virulence of different Candida species in both the planktonic and hyphal form and during the biofilm formation. This review focuses on the most recent findings that provide evidence of decreasing candidal pathogenicity by different substances of plant origin, with a special emphasis on the mechanisms of their action. This is a particularly important issue in the light of the currently increasing frequency of emerging Candida strains and species resistant to standard antifungal treatment.

The Interactions between the Antimicrobial Peptide P-113 and Living Candida albicans Cells Shed Light on Mechanisms of Antifungal Activity and Resistance

In the absence of proper immunity, such as in the case of acquired immune deficiency syndrome (AIDS) patients, Candida albicans, the most common human fungal pathogen, may cause mucosal and even life-threatening systemic infections. P-113 (AKRHHGYKRKFH), an antimicrobial peptide (AMP) derived from the human salivary protein histatin 5, shows good safety and efficacy profiles in gingivitis and human immunodeficiency virus (HIV) patients with oral candidiasis. However, little is known about how P-113 interacts with Candida albicans or its degradation by Candida-secreted proteases that contribute to the fungi’s resistance. Here, we use solution nuclear magnetic resonance (NMR) methods to elucidate the molecular mechanism of interactions between P-113 and living Candida albicans cells. Furthermore, we found that proteolytic cleavage of the C-terminus prevents the entry of P-113 into cells and that increasing the hydrophobicity of the peptide can significantly increase its antifungal activity. These results could help in the design of novel antimicrobial peptides that have enhanced stability in vivo and that can have potential therapeutic applications.

Candida albicans Shields the Periodontal Killer Porphyromonas gingivalis from Recognition by the Host Immune System and Supports the Bacterial Infection of Gingival Tissue

Candida albicans is a pathogenic fungus capable of switching its morphology between yeast-like cells and filamentous hyphae and can associate with bacteria to form mixed biofilms resistant to antibiotics. In these structures, the fungal milieu can play a protective function for bacteria as has recently been reported for C. albicans and a periodontal pathogen-Porphyromonas gingivalis. Our current study aimed to determine how this type of mutual microbe protection within the mixed biofilm affects the contacting host cells. To analyze C. albicans and P. gingivalis persistence and host infection, several models for host-biofilm interactions were developed, including microbial exposure to a representative monocyte cell line (THP1) and gingival fibroblasts isolated from periodontitis patients. For in vivo experiments, a mouse subcutaneous chamber model was utilized. The persistence of P. gingivalis cells was observed within mixed biofilm with C. albicans. This microbial co-existence influenced host immunity by attenuating macrophage and fibroblast responses. Cytokine and chemokine production decreased compared to pure bacterial infection. The fibroblasts isolated from patients with severe periodontitis were less susceptible to fungal colonization, indicating a modulation of the host environment by the dominating bacterial infection. The results obtained for the mouse model in which a sequential infection was initiated by the fungus showed that this host colonization induced a milder inflammation, leading to a significant reduction in mouse mortality. Moreover, high bacterial counts in animal organisms were noted on a longer time scale in the presence of C. albicans, suggesting the chronic nature of the dual-species infection.

Differential Abilities of Mammalian Cathelicidins to Inhibit Bacterial Biofilm Formation and Promote Multifaceted Immune Functions of Neutrophils

Mammalian cathelicidins act as the potent microbicidal molecules for controlling bacterial infection, and are considered promising alternatives to traditional antibiotics. Their ability to modulate host immune responses, as well as their bactericidal activities, is essential for therapeutic interventions. In this study, we compared the bactericidal activities, antibiofilm activities and immune-modulatory properties of cathelicidins BMAP-27, BMAP-34, mCRAMP, and LL-37, and evaluated the therapeutic efficacy of the combination of BMAP-27 and LL-37 using a mouse pulmonary infection model. Our results showed that all of the four cathelicidins effectively killed bacteria via rapid induction of membrane permeabilization, and BMAP-27 exhibited the most excellent bactericidal activity against diverse bacterial pathogens. BMAP-27, mCRAMP, and LL-37 effectively inhibited biofilm formation, while BMAP-34, mCRAMP and LL-37 exerted immunomodulatory functions with varying degrees of efficacy by stimulating the chemotaxis of neutrophils, inducing the production of reactive oxygen species, and facilitating the formation of neutrophil extracellular traps. Of note, the combination of BMAP-27 and LL-37 effectively enhanced the clearance of Pseudomonas aeruginosa and reduced the organ injury in vivo. Together, these findings highlight that identifying the appropriate synergistic combination of mammalian cathelicidins with different beneficial properties may be an effective strategy against bacterial infection.

Bacterial anti-microbial peptides and nano-sized drug delivery systems: The state of the art toward improved bacteriocins

Antimicrobial peptides (AMP) are molecules consisting of 12-100 amino acids synthesized by certain microbes and released extracellularly to inhibit the growth of other microbes. Among the AMP molecules, bacteriocins are produced by both gram-positive and gram-negative bacterial species and are used to kill or inhibit other prokaryotes in the environment. Due to their broad-spectrum antimicrobial activity, some bacteriocins have the potential of becoming the next generation of antibiotics for use in the crisis of multi antibiotic-resistant bacteria. Recently, bacteriocins have even been used to treat cancer. However, bacteriocins present a few drawbacks, such as sensitivity to proteases, immunogenicity issues, and the development of bacteriocin resistance by pathogenic bacteria. In this regard, nanoscale drug delivery systems (Nano-DDS) have led to the expectation that they will eventually improve the treatment of many diseases by addressing these limitations and improving bacteriocin pharmacokinetics and pharmacodynamics. Thus, combining bacteriocins with nano-DDS may be useful in overcoming these drawbacks and thereby reveal the full potential of bacteriocins. In this review article, we highlight the importance of tailoring nano-DDS to address bacteriocin limitations, the successes and failures of this technology thus far, the challenges that this technology still has to overcome before reaching the market, and future perspectives. Therefore, the purpose of this review is to highlight, categorize, compare and contrast the different nano-DDS described in the literature so far, and compare their effectiveness in order to improve the next generation of bacteriocin nano-sized drug delivery systems (Nano-DDS).

Nanoantibiotics containing membrane-active human cathelicidin LL-37 or synthetic ceragenins attached to the surface of magnetic nanoparticles as novel and innovative therapeutic tools: current status and potential future applications

Nanotechnology-based therapeutic approaches have attracted attention of scientists, in particular due to the special features of nanomaterials, such as adequate biocompatibility, ability to improve therapeutic efficiency of incorporated drugs and to limit their adverse effects. Among a variety of reported nanomaterials for biomedical applications, metal and metal oxide-based nanoparticles offer unique physicochemical properties allowing their use in combination with conventional antimicrobials and as magnetic field-controlled drug delivery nanocarriers. An ever-growing number of studies demonstrate that by combining magnetic nanoparticles with membrane-active, natural human cathelicidin-derived LL-37 peptide, and its synthetic mimics such as ceragenins, innovative nanoagents might be developed. Between others, they demonstrate high clinical potential as antimicrobial, anti-cancer, immunomodulatory and regenerative agents. Due to continuous research, knowledge on pleiotropic character of natural antibacterial peptides and their mimics is growing, and it is justifying to stay that the therapeutic potential of nanosystems containing membrane active compounds has not been exhausted yet.

The cysteine protease ApdS from Streptococcus suis promotes evasion of innate immune defenses by cleaving the antimicrobial peptide cathelicidin LL-37

Streptococcus suis is a globally distributed zoonotic pathogen associated with meningitis and septicemia in humans, posing a serious threat to public health. To successfully invade and disseminate within its host, this bacterium must overcome the innate immune system. The antimicrobial peptide LL-37 impedes invading pathogens by directly perforating bacterial membranes and stimulating the immune function of neutrophils, which are the major effector cells against S. suis However, little is known about the biological relationship between S. suis and LL-37 and how this bacterium adapts to and evades LL-37-mediated immune responses. In this study by using an array of approaches, including enzyme, chemotaxis, cytokine assays, quantitative RT-PCR, and CD spectroscopy, we found that the cysteine protease ApdS from S. suis cleaves LL-37 and thereby plays a key role in the interaction between S. suis and human neutrophils. S. suis infection stimulated LL-37 production in human neutrophils, and S. suis exposure to LL-37 up-regulated ApdS protease expression in the bacterium. We observed that ApdS targets and rapidly cleaves LL-37, impairing its bactericidal activity against S. suis We attributed this effect to the decreased helical content of the secondary structure in the truncated peptide. Moreover, ApdS rescued S. suis from killing by human neutrophils and neutrophil extracellular traps because LL-37 truncation attenuated neutrophil chemotaxis and inhibited the formation of extracellular traps and the production of reactive oxygen species. Altogether, our findings reveal an immunosuppressive strategy of S. suis whereby the bacterium blunts the innate host defenses via ApdS protease-mediated LL-37 cleavage.

"Candida Albicans Interactions With The Host: Crossing The Intestinal Epithelial Barrier"

Formerly a commensal organism of the mucosal surfaces of most healthy individuals, Candida albicans is an opportunistic pathogen that causes infections ranging from superficial to the more life-threatening disseminated infections, especially in the ever-growing population of vulnerable patients in the hospital setting. In these situations, the fungus takes advantage of its host following a disturbance in the host defense system and/or the mucosal microbiota. Overwhelming evidence suggests that the gastrointestinal tract is the main source of disseminated C. albicans infections. Major risk factors for disseminated candidiasis include damage to the mucosal intestinal barrier, immune dysfunction, and dysbiosis of the resident microbiota. A better understanding of C. albicans' interaction with the intestinal epithelial barrier will be useful for designing future therapies to avoid systemic candidiasis. In this review, we provide an overview of the current knowledge regarding the mechanisms of pathogenicity that allow the fungus to reach and translocate the gut barrier.

E-Cigarettes Increase Candida albicans Growth and Modulate its Interaction with Gingival Epithelial Cells

Electronic cigarette (e-cigarette) vapor comes in contact with the different constituents of the oral cavity, including such microorganisms as Candida albicans. We examined the impact of e-cigarettes on C. albicans growth and expression of different virulent genes, such as secreted aspartic proteases (SAPs), and the effect of e-cigarette vapor-exposed C. albicans on gingival epithelial cell morphology, growth, and lactate dehydrogenase (LDH) activity. An increase in C. albicans growth was observed with nicotine-rich e-cigarettes compared with non-exposed cultures. Following exposure to e-cigarette vapor, C. albicans produced high levels of chitin. E-cigarettes also increased C. albicans hyphal length and the expression of SAP2, SAP3, and SAP9 genes. When in contact with gingival epithelial cells, e-cigarette-exposed C. albicans adhered better to epithelial cells than the control. Indirect contact between e-cigarette-exposed C. albicans and gingival epithelial cells led to epithelial cell differentiation, reduced cell growth, and increased LDH activity. Overall, results indicate that e-cigarettes may interact with C. albicans to promote their pathogenesis, which may increase the risk of oral candidiasis in e-cigarette users.

Design of Antimicrobial Peptides: Progress Made with Human Cathelicidin LL-37

The incorporation of the innate immune system into humans is essential for survival and health due to the rapid replication of invading microbes and the delayed action of the adaptive immune system. Antimicrobial peptides are important components of human innate immunity. Over 100 such peptides have been identified in various human tissues. Human cathelicidin LL-37 is best studied, and there has been a growing interest in designing new peptides based on LL-37. This chapter describes the alternative processing of the human cathelicidin precursor, protease digestion, and lab cutting of LL-37. Both a synthetic peptide library and structure-based design are utilized to identify the active regions. Although challenging, the determination of the 3D structure of LL-37 enabled the identification of the core antimicrobial region. The minimal region of LL-37 can be function-dependent. We discuss the design and potential applications of LL-37 into antibacterial, antibiofilm, antiviral, antifungal, immune modulating, and anticancer peptides. LL-37 has been engineered into 17BIPHE2, a stable, selective, and potent antimicrobial, antibiofilm, and anticancer peptide. Both 17BIPHE2 and SAAP-148 can eliminate the ESKAPE pathogens and show topical in vivo antibiofilm efficacy. Also discussed are other application strategies, including peptide formulation, antimicrobial implants, and peptide-inducing factors such as vitamin D and sunlight. Finally, we summarize what we learned from peptide design based on human LL-37.

The Human Cathelicidin Antimicrobial Peptide LL-37 Promotes the Growth of the Pulmonary Pathogen Aspergillus fumigatus

The pulmonary mucus of cystic fibrosis (CF) patients displays elevated levels of the cathelicidin antimicrobial peptide LL-37, and the aim of this work was to assess the effect of LL-37 on the growth of Aspergillus fumigatus, a common pathogen of CF patients. Exposure of A. fumigatus to LL-37 and its derived fragment RK-31 (1.95 μg/ml) for 24 h had a positive effect on growth (199.94% ± 6.172% [P < 0.05] and 218.20% ± 4.63% [P < 0.05], respectively), whereas scrambled LL-37 peptide did not (85.12% ± 2.92%). Exposure of mycelium (preformed for 24 h) to 5 μg/ml intact LL-37 for 48 h increased hyphal wet weight (4.37 ± 0.23 g, P < 0.001) compared to the control (2.67 ± 0.05 g) and scrambled LL-37 (2.23 ± 0.09 g) treatments. Gliotoxin secretion from LL-37 exposed hyphae (169.1 ± 6.36 ng/mg hyphae, P < 0.05) was increased at 24 h compared to the results seen with the control treatment (102 ± 18.81 ng/mg hyphae) and the scrambled LL-37 treatment (96.09 ± 15.15 ng/mg hyphae). Shotgun proteomic analysis of 24-h LL-37-treated hyphae revealed an increase in the abundance of proteins associated with growth (eukaryotic translation initiation factor 5A [eIF-5A] [16.3-fold increased]), tissue degradation (aspartic endopeptidase [4.7-fold increased]), and allergic reactions (Asp F13 [10-fold increased]). By 48 h, there was an increase in protein levels indicative of cellular stress (glutathione peroxidase [9-fold increased]), growth (eIF-5A [6-fold increased]), and virulence (RNase mitogillin [3.7-fold increased]). These results indicate that LL-37 stimulates A. fumigatus growth and that this stimulation can result in increased fungal growth and secretion of toxins in the lungs of CF patients.

Fungicidal Potency and Mechanisms of θ-Defensins against Multidrug-Resistant Candida Species

Systemic candidiasis is a growing health care concern that is becoming even more challenging due to the growing frequency of infections caused by multidrug-resistant (MDR) Candida species. Thus, there is an urgent need for new therapeutic approaches to candidiasis, including strategies bioinspired by insights into natural host defense against fungal pathogens. The antifungal properties of θ-defensins, macrocyclic peptides expressed in tissues of Old World monkeys, were investigated against a panel of drug-sensitive and drug-resistant clinical isolates of Candida albicans and non-albicans Candida species. Rhesus θ-defensin 1 (RTD-1), the prototype θ-defensin, was rapidly and potently fungicidal against drug-sensitive and MDR C. albicans strains. Fungal killing occurred by cell permeabilization that was temporally correlated with ATP release and intracellular accumulation of reactive oxygen species (ROS). Killing by RTD-1 was compared with that by histatin 5 (Hst 5), an extensively characterized anticandidal peptide expressed in human saliva. RTD-1 killed C. albicans much more rapidly and at a >200-fold lower concentration than that of Hst 5. Unlike Hst 5, the anticandidal activity of RTD-1 was independent of mitochondrial ATP production. Moreover, RTD-1 was completely resistant to Candida proteases for 2 h under conditions that rapidly and completely degraded Hst 5. MICs and minimum fungicidal concentrations (MFCs) of 14 natural θ-defensins isoforms against drug-resistant C. albicans isolates identified peptides that are more active than amphotericin B and/or caspofungin against fluconazole-resistant organisms, including MDR Candida auris. These results point to the potential of macrocyclic θ-defensins as structural templates for the design of antifungal therapeutics.

The Effects of Antimicrobial Peptide Nal-P-113 on Inhibiting Periodontal Pathogens and Improving Periodontal Status

Periodontal disease consists of chronic gingival inflammation characterized by both degradation of the periodontal connective tissue and alveolar bone loss. Drug therapy is used as an auxiliary treatment method in severe chronic periodontitis, aggressive periodontitis, and periodontitis-associated systemic disease. Nal-P-113, a modified antimicrobial peptide, specifically replaces the histidine residues of P-113 with the bulky amino acid β-naphthylalanine, and our previous studies have verified that this novel peptide is not toxic to the human body within a certain concentration range. The objective of the present study was to evaluate the effect of Nal-P-113 on periodontal pathogens and periodontal status in clinical studies. In a split-mouth clinical trial, the pocket depth and bleeding index values tended to decrease in the experimental group compared with those in the control group. SEM results verified that Nal-P-113 restrained the maturation of plaque. Based on real-time polymerase chain reaction, the levels of Fusobacterium nucleatum, Streptococcus gordonii, Treponema denticola, and Porphyromonas gingivalis in subgingival plaque were decreased when the subjects were given Nal-P-113. Bacterial growth curve analysis and a biofilm susceptibility assay verified that Nal-P-113 at a concentration of 20 μg/mL restrained the growth of S. gordonii, F. nucleatum, and P. gingivalis and biofilm formation. Therefore, Nal-P-113 effectively reduces periodontal pathogens and ameliorates periodontal status.

Extracellular proteinases of Candida species pathogenic yeasts

The increased incidence of severe disseminated infections caused by the opportunistic yeast-like fungi Candida spp. highlights the urgent need for research into the major virulence factors of these pathogens-extracellular aspartic proteinases of the candidapepsin and yapsin families. Classically, these enzymes were considered to be generally destructive factors that damage host tissues and provide nutrients for pathogen propagation. However, in recent decades, novel and more specific functions have been suggested for extracellular candidal proteinases. These include contributions to cell wall maintenance and remodeling, the formation of polymicrobial biofilms, adhesion to external protective barriers of the host, the deregulation of host proteolytic cascades (such as the complement system, blood coagulation and the kallikrein-kinin system), a dysregulated host proteinase-inhibitor balance, the inactivation of host antimicrobial peptides, evasion of immune responses and the induction of inflammatory mediator release from host cells. Only a few of these activities recognized in Candida albicans candidapepsins have been also confirmed in other Candida species, and characterization of Candida glabrata yapsins remains limited.

Perspectives for clinical use of engineered human host defense antimicrobial peptides

Infectious diseases caused by bacteria, viruses or fungi are among the leading causes of death worldwide. The emergence of drug-resistance mechanisms, especially among bacteria, threatens the efficacy of all current antimicrobial agents, some of them already ineffective. As a result, there is an urgent need for new antimicrobial drugs. Host defense antimicrobial peptides (HDPs) are natural occurring and well-conserved peptides of innate immunity, broadly active against Gram-negative and Gram-positive bacteria, viruses and fungi. They also are able to exert immunomodulatory and adjuvant functions by acting as chemotactic for immune cells, and inducing cytokines and chemokines secretion. Moreover, they show low propensity to elicit microbial adaptation, probably because of their non-specific mechanism of action, and are able to neutralize exotoxins and endotoxins. HDPs have the potential to be a great source of novel antimicrobial agents. The goal of this review is to provide an overview of the advances made in the development of human defensins as well as the cathelicidin LL-37 and their derivatives as antimicrobial agents against bacteria, viruses and fungi for clinical use.

Engineering improved variants of the antifungal peptide histatin 5 with reduced susceptibility to Candida albicans secreted aspartic proteases and enhanced antimicrobial potency

Candida albicans is an opportunistic fungal pathogen and a commensal organism that commonly colonizes mucosal surfaces, including those inside the human mouth. To help control C. albicans, human saliva contains the antifungal peptide histatin 5 (Hst-5), which has strong antifungal activity against C. albicans. However, the pathogen produces secreted aspartic proteases (Saps) that cleave Hst-5 at lysine residues and eliminate its antifungal properties. We designed variants of Hst-5 with its lysine residues substituted with arginine or leucine to evaluate the effect on proteolysis by Saps. We found site-, residue-, and Sap-dependent effects from single amino acid substitutions. The K17R and K17L modifications led to dramatic results, with over 77% and 100% intact peptide remaining after incubation with Sap9 and Sap2, respectively, compared to 47% and 61% of Hst-5. This decrease in proteolysis was accompanied by a reduction in cleavage on the C-terminal side of K17, suggesting the Saps prefer lysine at K17 for cleavage. Incubation with C. albicans cells and culture supernatant corroborated the results with purified Saps and highlighted their biological relevance. The modifications to Hst-5 do not diminish the antifungal activity of Hst-5, and, in fact, the K17R, K17L, and K11R peptides retained significantly more antifungal activity after treatment with Saps than Hst-5. Our results indicate that single amino acid modifications drastically impact both proteolysis at the modification sites and the overall level of proteolysis of the peptide, demonstrating the potential of designing peptides for resistance to proteolysis as a means for improving therapeutic efficacy.

Innate Immunity to Mucosal Candida Infections

Mucosal epithelial tissues are exposed to high numbers of microbes, including commensal fungi, and are able to distinguish between those that are avirulent and those that cause disease. Epithelial cells have evolved multiple mechanisms to defend against colonization and invasion by Candida species. The interplay between mucosal epithelial tissues and immune cells is key for control and clearance of fungal infections. Our understanding of the mucosal innate host defense system has expanded recently with new studies bringing to light the importance of epithelial cell responses, innate T cells, neutrophils, and other phagocytes during Candida infections. Epithelial tissues release cytokines, host defense peptides, and alarmins during Candida invasion that act in concert to limit fungal proliferation and recruit immune effector cells. The innate T cell/IL-17 axis and recruitment of neutrophils are of central importance in controlling mucosal fungal infections. Here, we review current knowledge of the innate immunity at sites of mucosal Candida infection, with a focus on infections caused by C. albicans.

Aspartic Proteases and Major Cell Wall Components in Candida albicans Trigger the Release of Neutrophil Extracellular Traps

Neutrophils use different mechanisms to cope with pathogens that invade the host organism. The most intriguing of these responses is a release of neutrophil extracellular traps (NETs) composed of decondensed chromatin and granular proteins with antimicrobial activity. An important potential target of NETs is Candida albicans-an opportunistic fungal pathogen that employs morphological and phenotype switches and biofilm formation during contact with neutrophils, accompanied by changes in epitope exposition that mask the pathogen from host recognition. These processes differ depending on infection conditions and are thus influenced by the surrounding environment. In the current study, we compared the NET release by neutrophils upon contact with purified main candidal cell surface components. We show here for the first time that in addition to the main cell wall-building polysaccharides (mannans and β-glucans), secreted aspartic proteases (Saps) trigger NETs with variable intensities. The most efficient NET-releasing response is with Sap4 and Sap6, which are known to be secreted by fungal hyphae. This involves mixed, ROS-dependent and ROS-independent signaling pathways, mainly through interactions with the CD11b receptor. In comparison, upon contact with the cell wall-bound Sap9 and Sap10, neutrophils responded via a ROS-dependent mechanism using CD16 and CD18 receptors for protease recognition. In addition to the Saps tested, the actuation of selected mediating kinases (Src, Syk, PI3K, and ERK) was also investigated. β-Glucans were found to trigger a ROS-dependent process of NET production with engagement of Dectin-1 as well as CD11b and CD18 receptors. Mannans were observed to be recognized by TLRs, CD14, and Dectin-1 receptors and triggered NET release mainly via a ROS-independent pathway. Our results thus strongly suggest that neutrophils activate NET production in response to different candidal components that are presented locally at low concentrations at the initial stages of infection. However, NET release seemed to be blocked by increasing numbers of fungal cells.

Formulation and candidacidal activity of magnetic nanoparticles coated with cathelicidin LL-37 and ceragenin CSA-13

Fungal infections caused by Candida spp. represent an emerging problem during treatment of immunocompromised patients and those hospitalized with serious principal diseases. The ever-growing number of fungal strains exhibiting drug resistance necessitates the development of novel antimicrobial therapies including those based on membrane-permeabilizing agents and nanomaterials as drug carriers. In this study, the fungicidal activities of LL-37 peptide, ceragenin CSA-13 and its magnetic derivatives (MNP@LL-37, MNP@CSA-13) against laboratory and clinical strains of C. albicans, C. glabrata and C. tropicalis were evaluated. These experiments confirm the high anti-fungal activity of these well-characterized agents mediated by their interaction with the fungal membrane and demonstrate elevated activity following immobilization of LL-37 and CSA-13 on the surface of magnetic nanoparticles (MNPs). Furthermore, MNP-based nanosystems are resistant to inhibitory factors present in body fluids and effectively inhibit formation of fungal biofilm. Simultaneously, synthesized nanostructures maintain immunomodulatory properties, described previously for free LL-37 peptide and CSA-13 substrate and they do not interfere with the proliferation and viability of osteoblasts, confirming their high biocompatibility.

Antifungal Resistance, Metabolic Routes as Drug Targets, and New Antifungal Agents: An Overview about Endemic Dimorphic Fungi

Diseases caused by fungi can occur in healthy people, but immunocompromised patients are the major risk group for invasive fungal infections. Cases of fungal resistance and the difficulty of treatment make fungal infections a public health problem. This review explores mechanisms used by fungi to promote fungal resistance, such as the mutation or overexpression of drug targets, efflux and degradation systems, and pleiotropic drug responses. Alternative novel drug targets have been investigated; these include metabolic routes used by fungi during infection, such as trehalose and amino acid metabolism and mitochondrial proteins. An overview of new antifungal agents, including nanostructured antifungals, as well as of repositioning approaches is discussed. Studies focusing on the development of vaccines against antifungal diseases have increased in recent years, as these strategies can be applied in combination with antifungal therapy to prevent posttreatment sequelae. Studies focused on the development of a pan-fungal vaccine and antifungal drugs can improve the treatment of immunocompromised patients and reduce treatment costs.

Cathelicidin-trypsin inhibitor loop conjugate represents a promising antibiotic candidate with protease stability

Cathelicidins are regarded as promising antibiotics due to their capability against antibiotic-resistant bacteria without cytotoxicity. However, some concerns about the balance of cytotoxicity and antimicrobial activity, weak stability and enzymatic susceptibility sually restrict their therapeutic use. Here, we designed a series of shortened variants, Hc1~15, based on our previously characterized Hc-CATH. Hc3, the one with the best activity, after point mutation was engineered with a trypsin inhibitor loop, ORB-C, to obtain four hybrid peptides: H3TI, TIH3, H3TIF and TIH3F. All four except TIH3 were found possessing an appreciable profile of proteases inhibitory and antimicrobial characteristics without increase in cytotoxicity. Among them, TIH3F exhibited the most potent and broad-spectrum antimicrobial and anti-inflammatory activities. Fluorescence spectroscopy has demonstrated a quick induction of bacterial membrane permeability by TIH3F leading to the cell death, which also accounts for its fast anti-biofilm activity. Such mode of antimicrobial action was mainly attributed to peptides’ amphiphilic and helical structures determined by CD and homology modeling. Besides, TIH3F exhibited good tolerance to salt, serum, pH, and temperature, indicating a much better physiological stability in vitro than Hc3, Most importantly, in the case of resistance against proteases hydrolysis, current hybrid peptides displayed a remarkable enhancement than their original templates.

Immunity to Commensal Fungi: Detente and Disease

Fungi are ubiquitous in our environment, and a healthy immune system is essential to maintain adequate protection from fungal infections. When this protection breaks down, superficial and invasive fungal infections cause diseases that range from irritating to life-threatening. Millions of people worldwide develop invasive infections during their lives, and mortality for these infections often exceeds 50%. Nevertheless, we are normally colonized with many of the same disease-causing fungi (e.g., on the skin or in the gut). Recent research is dramatically expanding our understanding of the mechanisms by which our immune systems interact with these organisms in health and disease. In this review, we discuss what is currently known about where and how the immune system interacts with common fungi.

Candidacidal Activity of Selected Ceragenins and Human Cathelicidin LL-37 in Experimental Settings Mimicking Infection Sites

Fungal infections, especially those caused by antibiotic resistant pathogens, have become a serious public health problem due to the growing number of immunocompromised patients, including those subjected to anticancer treatment or suffering from HIV infection. In this study we assessed fungicidal activity of the ceragenins CSA-13, CSA-131 and CSA-192 against four fluconazole–resistant Candida strains. We found that ceragenins activity against planktonic Candida cells was higher than activity of human LL-37 peptide and synthetic cationic peptide omiganan. Compared to LL-37 peptide, ceragenins in the presence of DNase I demonstrated an increased ability to kill DNA-induced Candida biofilm. Microscopy studies show that treatment with LL-37 or ceragenins causes Candida cells to undergo extensive surface changes indicating surface membrane damage. This conclusion was substantiated by observation of rapid incorporation of FITC-labeled CSA-13, CSA-131 or LL-37 peptide into the more lipophilic environment of the Candida membrane. In addition to activity against Candida spp., ceragenins CSA-131 and CSA-192 display strong fungicidal activity against sixteen clinical isolates including Cryptococcus neoformans and Aspergillus fumigatus. These results indicate the potential of ceragenins for future development as new fungicidal agents.

Pollution of mycological surfaces in hospital emergency departments correlates positively with blood NKT CD3(+) 16(+) 56(+) and negatively with CD4(+) cell levels of their staff

The aim of the present study was the assessment of the putative influence of yeast and filamentous fungi in healthcare and control (office) workplaces (10 of each kind) on immune system competence measured by NK (natural killer), CD4⁺, and NKT (natural killer T lymphocyte) cell levels in the blood of the personnel employed at these workplaces.

Imprints from floors and walls were collected in winter. The blood was taken in spring the following year, from 40 men, 26 to 53 years old, healthcare workers of hospital emergency departments (HED), who had been working for at least five years in their current positions, and from 36 corresponding controls, working in control offices. Evaluation of blood leukocyte subpopulations was done by flow cytometry. The qualitative analysis of the surface samples revealed a prevalence of strains belonging to Aspergillus spp. and Penicillium spp. genus. There was no statistically significant difference between the level of NKT; however, the percentage of NK cells was lower in the blood of HED workers than in the blood of offices personnel. Spearman analysis revealed the existence of positive correlation (r = 0.4677, p = 0.002) between the total CFU/25 cm² obtained by imprinting method from walls and floors of HED and the percentage of NKT (CD3⁺16⁺56⁺) lymphocytes collected from the blood of their personnel, and negative correlation (r = –0. 3688, p = 0.019) between this parameter of fungal pollution and the percentage of CD4⁺ lymphocytes in the blood of HED staff. No other correlations were found.

Autonomous immunity in mucosal epithelial cells: fortifying the barrier against infection

Mucosal epithelial cells express an autonomous innate immune response that controls the overgrowth of invaded bacteria, mitigates the harmful effects of the bacteria carried within, and does not rely on other external arms of the immune response. Epithelial cell autonomous innate immunity "respects" the social biology of invading bacteria to achieve symbiosis, and is the primary protective mechanism against pathogens.

Management of Candida biofilms: state of knowledge and new options for prevention and eradication

Biofilms formed by Candida species (spp.) on medical devices represent a potential health risk. The focus of current research is searching for new options for the treatment and prevention of biofilm-associated infections using different approaches including modern nanotechnology. This review summarizes current information concerning the most relevant resistance/tolerance mechanisms to conventional drugs and a role of additional factors contributing to these phenomena in Candida spp. (mostly Candida albicans). Additionally, it provides an information update in prevention and eradication of a Candida biofilm including experiences with 'lock' therapy, potential utilization of small molecules in biomedical applications, and perspectives of using photodynamic inactivation in the control of a Candida biofilm.

Role of Candida albicans secreted aspartyl protease Sap9 in interkingdom biofilm formation

The fungus Candida albicans colonizes oral cavity surfaces and is carried by up to 60% of human populations. Biofilm development by C. albicans may be modulated by oral streptococci, such as Streptococcus gordonii, S. oralis or S. mutans, so as to augment pathogenicity. In this study we sought to determine if the cell wall-associated secreted aspartyl proteinase Sap9 was necessary for hyphal adhesin functions associated with biofilm community development. A sap9Δ mutant of C. albicans SC5314 formed biofilms that were flatter, and contained fewer blastospores and more hyphal filaments than the parent strain. This phenotypic difference was accentuated under flow (shear) conditions and in the presence of S. gordonii. Dual-species biofilms of C. albicans sap9Δ with S. oralis, S. sanguinis, S. parasanguinis, S. mutans and Enterococcus faecalis all contained more matted hyphae and more bacteria bound to substratum compared to C. albicans wild type. sap9Δ mutant hyphae showed significantly increased cell surface hydrophobicity, ∼25% increased levels of binding C. albicans cell wall protein Als3, and reduced interaction with Eap1, implicating Sap9 in fungal cell-cell recognition. These observations suggest that Sap9 is associated with protein-receptor interactions between fungal cells, and with interkingdom communication in the formation of polymicrobial biofilm communities.

Design and studies of multiple mechanism of anti-Candida activity of a new potent Trp-rich peptide dendrimers

PURPOSE

Eight peptide dendrimers were designed as structural mimics of natural cationic amphiphilic peptides with antifungal activity and evaluated for their anti-Candida potential against the wild type strains and mutants.

METHODS

Dendrimer 14 containing four Trp residues and dodecyl tail and a slightly smaller dendrimer 9 decorated with four N-methylated Trp that displayed 100 and 99.7% of growth inhibition at 16 μg/mL respectively, were selected for evaluation against the Candida albicans mutants with disabled biosynthesis of aspartic proteases responsible for host tissue colonization and morphogenesis during biofilm formation (sessile model). Flow cytometry method was employed to detect apoptotic cells with membrane alterations (phosphatidylserine translocation), and differentiation of apoptotic from necrotic cells was also performed. Simultaneous staining of cell surface phosphatidylserine with Annexin-V-Fluorescein and necrotic cells with propidium iodide was conducted.

RESULTS

14 at 16 μg/mL caused C. albicans cells to undergo cellular apoptosis but its increasing concentrations induced necrosis. 14 influenced C. albicans biofilm viability as well as hyphal and cell wall morphology. Confocal microscopy and cell wall staining with calcofluor white revealed that in epithelial model the cell surface structure was perturbed at MIC of peptide dendrimer. It appears that tryptophan or 1-methyltryptophan groups displayed at the surface and positive charges hidden in the dendrimer tree along with hydrocarbon tail located at C-terminus are important for the anti-Candida activity since dendrimers containing tryptamine at C-terminus showed only a moderate activity.

CONCLUSIONS

Our results suggest that membranolytic dendrimer 14, targeting cellular apoptotic pathway and impairing the cell wall formation in mature biofilm, may be a potential multifunctional antifungal lead compound for the control of C. albicans infections.

Antifungal activity of cathelicidin peptides against planktonic and biofilm cultures of Candida species isolated from vaginal infections

Vulvovaginal candidiasis (VVC) is a frequent gynecological condition caused by Candida albicans and a few non-albicans Candida spp. It has a significant impact on the quality of life of the affected women also due to a considerable incidence of recurrent infections that are difficult to treat. The formation of fungal biofilm may contribute to the problematic management of recurrent VVC due to the intrinsic resistance of sessile cells to the currently available antifungals. Thus, alternative approaches for the prevention and control of biofilm-related infections are urgently needed. In this regard, the cationic antimicrobial peptides (AMPs) of the innate immunity are potential candidates for the development of novel antimicrobials as many of them display activity against biofilm formed by various microbial species. In the present study, we investigated the in vitro antifungal activities of the cathelicidin peptides LL-37 and BMAP-28 against pathogenic Candida spp. also including C. albicans, isolated from vaginal infections, and against C. albicans SC5314 as a reference strain. The antimicrobial activity was evaluated against planktonic and biofilm-grown Candida cells by using microdilution susceptibility and XTT [2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide] reduction assays and, in the case of established biofilms, also by CFU enumeration and fluorescence microscopy. BMAP-28 was effective against planktonically grown yeasts in standard medium (MIC range, 2-32μM), and against isolates of C. albicans and Candida krusei in synthetic vaginal simulated fluid (MIC range 8-32μM, depending on the pH of the medium). Established 48-h old biofilms formed by C. albicans SC5314 and C. albicans and C. krusei isolates were 70-90% inhibited within 24h incubation with 16μM BMAP-28. As shown by propidium dye uptake and CFU enumeration, BMAP-28 at 32μM killed sessile C. albicans SC5314 by membrane permeabilization with a faster killing kinetics compared to 32μM miconazole (80-85% reduced biofilm viability in 90min vs 48h). In addition, BMAP-28 at 16μM prevented Candida biofilm formation on polystyrene and medical grade silicone surfaces by causing a >90% reduction in the viability of planktonic cells in 30min. LL-37 was overall less effective than BMAP-28 against planktonic Candida spp. (MIC range 4-≥64μM), and was ineffective against established Candida biofilms. However, LL-37 at 64μM prevented Candida biofilm development by inhibiting cell adhesion to polystyrene and silicone surfaces. Finally, Candida adhesion was strongly inhibited when silicone was pre-coated with a layer of BMAP-28 or LL-37, encouraging further studies for the development of peptide-based antimicrobial coatings.