Mode of action of plant defensins suggests therapeutic potential

Higher vertebrates can rely both on an innate as well as an adaptive immune system for defense against invading pathogens. In contrast, plants can only employ an innate immune system that largely depends on the production of antimicrobial compounds such as plant defensins and other pathogenesis-related proteins. Plant defensins are ubiquitous, cationic, cysteine-rich plant peptides and have a folding pattern that shares high similarity to defense peptides of mammals and insects, suggesting an ancient and conserved origin. A large number of plant defensins appear to display antifungal activity. Some of these defensins have been found to interact with fungal-specific components in the plasmamembrane, resulting in membrane permeabilization. This makes them an attractive source of potential therapeutics to treat fungal infections.     

Fungal sphingolipids as targets for the development of selective antifungal therapeutics

Sphingolipids are essential membrane components, present in all eukaryotic cells, but structurally distinct in mammalian and fungal cells. Therefore, they represent an attractive new target for the development of novel antimycotics. This review will briefly highlight sphingolipid biosynthesis and functions in the yeast Saccharomyces cerevisiae. In addition, naturally occurring antifungal compounds that interact with fungal-specific sphingolipids, resulting in fungal growth arrest, will be discussed regarding their mode of action, and therapeutic value. These compounds include plant and insect defensins, syringomycin E and antifungal antibodies to sphingolipids.     

Antimicrobial activity of clove oil and its potential in the treatment of vaginal candidiasis

In the present study, we evaluated antimicrobial activity of clove oil against a range of fungal pathogens including that responsible for urogenital infection. Clove oil was found to possess strong antifungal activity against opportunistic fungal pathogens such as Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus, etc. The oil was found to be extremely successful in the treatment of experimental murine vaginitis in model animals. On evaluating various formulations, topical administration of the liposomized clove oil was found to be most effective against treatment of vaginal candidiasis.     

Antimicrobial activity of clove oil and its potential in the treatment of vaginal candidiasis

In the present study, we evaluated antimicrobial activity of clove oil against a range of fungal pathogens including that responsible for urogenital infection. Clove oil was found to possess strong antifungal activity against opportunistic fungal pathogens such as Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus, etc. The oil was found to be extremely successful in the treatment of experimental murine vaginitis in model animals. On evaluating various formulations, topical administration of the liposomized clove oil was found to be most effective against treatment of vaginal candidiasis.     

Antimicrobial peptides: therapeutic potential for the treatment of Candida infections

The increasing frequency of fungal infections in immunocompromised patients together with the emergence of strains resistant to currently used antifungal drugs point to an increased need for a new class of antimycotics. Antimicrobial peptides are promising candidates for the treatment of fungal infections since they have both mechanisms of action distinct from available antifungal agents and the ability to regulate the host immune defence systems as well. This review focuses on Candida albicans as a large amount of work on the mechanisms of action of classical antifungals as well as antimicrobial peptides, such as defensins, protegrins, histatins and lactoferrin (LF)-derived peptides, has been performed in this yeast. Analogues of these antimicrobial peptides and combinations of antimicrobial peptides with classical antimycotics are under investigation for treatment of candidiasis.     

Detection of fungal infections using radiolabeled antifungal agents

The outcome of antifungal therapy depends on the progression of the infection at the start of therapy. Unfortunately, most patients are diagnosed once the fungal infection has progressed considerably as a result of the non-specific clinical signs of fungal infections in immunocompromised patients and the poor sensitivity of current mycological diagnostic tests. This review will highlight current fungal diagnostic techniques and will focus on scintigraphic methods for the specific detection of fungal infections in mice. For this purpose, antifungal components (e.g. fluconazole and antifungal peptides) are radiolabeled e.g. with technetium-99m ((99m)Tc) and their in vivo distribution is monitored in infected mice. It has been demonstrated that (99m)Tc-fluconazole is an excellent tracer to detect Candida albicans infections in mice as it distinguishes these infections from bacterial infections and sterile inflammations. However, this radiopharmaceutical only poorly detects infections with Aspergillus fumigatus in mice. (99m)Tc-peptides derived from antifungal peptides/proteins, such as human ubiquicidin and lactoferrin, can distinguish C. albicans and A. fumigatus infections from sterile inflammations, but not from bacterial infections, in mice. Furthermore, the efficacy of fluconazole in C. albicans-infected mice could be successfully monitored using (99m)Tc-ubiquicidin. In conclusion, neither (99m)Tc-fluconazole nor the (99m)Tc-peptides tested are optimal tracers for fungal infections. Nonetheless, since early initiation of antifungal therapy for candidemia reduces its high mortality rate, a positive result with (99m)Tc-fluconazole scintigraphy is of clinical relevance. Finally, the possibility that other (radiolabeled) antifungal agents, e.g. voriconazole, caspofungin, antifungal plant or insect defensins, can be useful for detection of fungal infections should be considered.     

Antibacterial and antifungal activities of extracts of combretum molle

OBJECTIVE: In traditional medical practices of Ethiopia the aqueous extracts obtained from the stem bark of Combretum molle (R. Br. Ex. G. Don.) Engl & Diels (Combretaceae) have a longstanding reputation for the treatment of liver diseases malaria and tuberculosis. Owing to the widespread traditional uses of this plant, the studyinvestigated the antimicrobial activity the bark extract of this plant against Gram positive and and Gram negative bacteria. METHODS: Petroleum ether, dichloromethane and acetone fractions of the bark of the plant were prepared by soxhlet extraction and screened for their antimicrobial activity. The acetone fraction exhibited a powerful activity and was therefore further tested against twenty-one bacterial and six fungal strains. The minimum inhibitory concentration (MIC) of this extract was determined by checker board technique using nutrient agar medium. The zones of inhibition produced by the extract against bacteria and fungi were determined and compared by disc diffusion technique with those of pure ciprofloxacin and griseofulvin, respectively. RESULTS: The highest antibacterial action of the acetone extract was against the Gram negative organisms EscherIchia coli and Shigella spp with an MIC value of 50 mg/ml. The activity of the extract against these bacteria was comparable to that of ciprofloxacin when assessed by the disc diffusion technique. Among the fungal strains tested Candida albicans showed high susceptibility to the extract and growth was completely inhibited at a concentration of 400 microg/ml. At the same concentration, the acetone extract and the standard antifungal drug griseofulvin produced comparable zones of inhibition on C. albicans. Studies on the mode of action of the extract indicated that it was bactericidal and fungicidal. The antimicrobial activity of the extract was attributed to the high amount of hydrolysable tannins present in the bark of the plant. CONCLUSION: The acetone extract of the stem bark of C. molle has the potential for use as a natural antimicrobial agent. Further in vivo antimicrobial, phytochemical and toxicological studies are requireed to evaluate the chemotherapeutic effect of the plant.     

Fungal biofilms and antimycotics

Device-related infections in most nosocomial diseases can be traced to the formation of biofilms (microbial communities encased within a polysaccharide-rich extracellular matrix) by pathogens on surfaces of these devices. Candida species are the most common causative agents of these infections, and biofilms formed by these fungal organisms are associated with drastically enhanced resistance against most antimicrobial agents. This enhanced resistance contributes to the persistence of this fungus despite antifungal therapy. Recent studies showed that Candida biofilms exhibit antifungal resistance against most antifungal agents with the exception of echinocandins and lipid formulations of AMB. This review discusses methods used to evaluate biofilm resistance and provide information on susceptibility pattern of candidal biofilm as well as studies investigating the mechanisms underlying biofilm resistance.     

Treatment of invasive infections due to rare or emerging yeasts and moulds

Emerging fungal infections represent a serious problem in an immunocompromised host. Rapid developments in in vitro antifungal susceptibility testing and the availability of several new antifungal agents have provided excellent opportunities to treat infections that are caused by various Candida spp. and to some extend by Aspergillus spp. However, recently the epidemiology of fungal infections has significantly changed and several new pathogens have emerged. This article attempts to summarise the available data on the management of emerging infections with fungal infections that have recently gained importance. Updated recommendations on antifungal treatment are also discussed.     

Design and synthesis of amphipathic antimicrobial peptides

A large proportion of antimicrobial peptides share a common structural feature that is critical to their antimicrobial activity, i.e. amphipathic α-helices. The amphipathy of a polypeptide chain can be quantitated through the value of the hydrophobic moment. Generally, antimicrobial peptides are characterized by high hydrophobic moment and low hydrophobicity values. Using these criteria we have identified two short segments that possess hydrophobic moment properties associated with known antimicrobial peptides. Using in vitro assays the segment derived from the protein perforin displays no antifungal or antibacterial activity and, while showing no α-helicity in buffer or liposomes, exhibits a modest degree of α-helical structure in the presence of the a-helical inducer, 2,2,2-trifluoroethanol. However, rational modifications result in a derivative which assumes an α-helical conformation in the presence of liposomes, exhibits potent antifungal activity against plant fungal pathogens, has significant antibacterial activity, effects leakage of a fluorescent dye from acidic liposomes and is devoid of hemolytic activity. Results are also presented for a segment derived from the human immunodeficiency virus envelope protein. We suggest that the identification of putative amphipathic structures in proteins may provide a useful starting strategy in the design and synthesis of antimicrobial peptides.     

A new nonadride derivative, dihydroepiheveadride, as characteristic antifungal agent against filamentous fungi, isolated from unidentified fungus IFM 52672

In the screening of searching for new antifungal agents, a new nonaride compound, dihydroepiheveadride (1), was isolated from unidentified fungus IFM 52672 as the most potent antifungal principle from this organism. The structure of 1 was established on the basis of spectroscopic and chemical investigation, as well as detailed comparison of the spectroscopic and physico-chemical data of the oxidized derivative (3) from 1 with those of heveadride (2). Compound 1 showed strong antifungal activity against various filamentous fungi including human pathogens Aspergillus fumigatus, Penicillium marneffei and Trichophyton spp. It also showed the growth inhibition activity against certain human pathogenic yeasts such as Trichosporon species, while it had weak or no antifungal activity against Candida spp. and Cryptococcus neoformans, and no antibacterial activity against Bacillus subtilis nor against Escherichia coli. The antifungal potencies of compounds 2 and 3 were found to be weaker than that of 1.     

Expression of defensins in gingiva and their role in periodontal health and disease

Oral epithelium is a stratified squamous epithelium that functions as the barrier between the outside environment and the host. In the oral cavity, epithelial tissues are constantly exposed to a variety of bacteria, but most individuals maintain healthy homeostasis. Epithelial cells contribute to the innate host response, and antimicrobial peptide expression in all human epithelia, including oral epithelia, is an important part of this epithelial function. These antimicrobial peptides have a broad spectrum of activity against both Gram-negative and Gram-positive bacteria as well as against yeast and viruses. In humans these antimicrobial peptides include defensins and a cathelicidin family member LL-37 in skin and oral mucosa and other epithelia. The human defensins include the alpha-defensins of intestinal and neutrophil origin, and the beta-defensins of skin and oral mucosa and other epithelia. Present studies have identified specific signaling routes that pathogens and commensals take in stimulating these innate immune responses, and this may open the way for development of new therapeutic agents for periodontal diseases.     

Severe Candida spp. infections: new insights into natural immunity

Invasive infections caused by Candida spp. are associated with high mortality. Colonisation by Candida spp. and the capacity of the host to recognise them as potential pathogens are essential steps in the development of these infections. The major pathogen-associated molecular patterns of Candida are mannoproteins, glucans and chitins, which are recognised by C-type lectin pattern recognition receptors such as the mannose receptor, dectin-1 and dectin-2. By the secretion of proteases and toxins, and the formation of hyphae and biofilms, Candida spp. are able to enhance their virulence and pathogenicity. Studies in patients with relatively rare immunodeficiencies, such as dectin-1 deficiency, CARD9 deficiency, chronic mucocutaneous candidiasis, hyper-IgE/Job's syndrome and chronic granulomatous disease, have shown the role of dectin-1 and its signalling pathway, which involves interleukins 17 and 22, defensins and phagocytic cells, in defence against Candida. These studies also provide insights into how acquired risk factors for fungal infection operate, and may lead to new approaches for immunotherapy.     

医院内MRSA肺炎多重病原体感染及其药敏分析

探讨医院内 MRSA肺炎严重混合感染的病原体分布及其对常用抗生素药物敏感性。选择本实验室近 4年来确诊医院内 MRSA肺炎病人痰标本分离的致病菌 ,采用 K- B纸片及 E- test方法分别检测混合感染细菌和真菌对常用抗生素的体外敏感性。结果 6 4例次院内混合感染病原体中细菌 46例次占 71.88% ,真菌 18例占 2 8.13%。细菌对 13种常见抗生素呈现不同程度的严重耐药。其中除曲霉耐氟康唑外 ,部分白念珠菌也出现耐药 ,伊曲康唑和两性霉素 B效果较好。提示医院内 MRSA肺炎常合并多重高度耐药菌感染 ,治疗困难 ,必须进行严格的细菌学分析和耐药监测 ,及时选用有效抗生素。     

Posaconazole : a review of its use in the prophylaxis of invasive fungal infections

Posaconazole is a second-generation triazole antifungal agent with a broad spectrum of activity that includes Aspergillus spp., Candida spp. and the Zygomycetes. In the US, posaconazole oral suspension administered three times daily is indicated for prophylaxis against invasive Aspergillus and Candida infections in patients aged > or =13 years who are at high risk of developing these infections because of immunosuppression, such as haematopoietic stem cell transplant (HSCT) recipients with graft-versus-host disease (GVHD), or those with haematological malignancies with prolonged neutropenia as a result of chemotherapy. EU-approved prophylactic indications for posaconazole are similar to those in the US.Posaconazole provided effective prophylaxis against invasive fungal infections and was generally well tolerated in two large, well designed trials in HSCT recipients with GVHD, or patients receiving induction-remission chemotherapy for acute myeloid leukaemia (AML) or myelodysplastic syndrome (MDS) that was expected to result in prolonged neutropenia. It offers coverage of clinically relevant pathogens and is potentially associated with fewer drug-drug interactions than other licensed triazole antifungal agents. Its usefulness in some patients may be limited by the lack of an intravenous formulation, although one is currently being developed. As with other antifungal agents, concerns remain regarding the potential emergence of resistance to broad-spectrum antifungal prophylaxis with posaconazole. Despite this, posaconazole is a valuable emerging option for use as prophylaxis against invasive fungal infections in immunocompromized patients who are at high risk of developing these infections.     

Treatment of invasive infections due to rare or emerging yeasts and moulds

Emerging fungal infections represent a serious problem in an immunocompromised host. Rapid developments in in vitro antifungal susceptibility testing and the availability of several new antifungal agents have provided excellent opportunities to treat infections that are caused by various Candida spp. and to some extend by Aspergillus spp. However, recently the epidemiology of fungal infections has significantly changed and several new pathogens have emerged. This article attempts to summarise the available data on the management of emerging infections with fungal infections that have recently gained importance. Updated recommendations on antifungal treatment are also discussed.     

Activity of pradimicin BMS-181184 against Aspergillus spp.

The pradimicins are a new class of antifungal agents with activity against the majority of human fungal pathogens. In this study, the in vitro activity of pradimicin BMS-181184 was investigated against a range of the most common species of Aspergillus. The results were compared with itraconazole and amphotericin B. BMS-181184 was found to be active against most Aspergillus spp., but at higher concentrations than itraconazole and amphotericin B.     

In vitro antifungal activity of posaconazole against various pathogenic fungi

The antifungal activity of posaconazole (SCH56592), a new triazole antifungal, against stock cultures and fresh clinical isolates of a wide range of pathogenic fungi was compared with that of itraconazole, fluconazole and amphotericin B. Posaconazole inhibited growth of all the fungal species tested except Fusarium spp. at 1 mg/l or lower concentrations, showing a broad-spectrum antifungal activity. The activities of posaconazole for all the fungal species far surpassed those of fluconazole and were even superior to those of itraconazole for Aspergillus spp. as well as for many other fungal species.     

β-sheet antibiotic peptides as potential dental therapeutics

Small, cysteine-rich, β-sheet peptide antibiotics are found throughout the Animalia. Though broad spectrum in potential, they may exert selective antimicrobial effects under certain conditions. We have explored the antimicrobial properties of two families of β-sheet peptide antibiotics, defensins and protegrins, against periodontopathic bacteria. The rabbit defensin NP-1 was active against facultative Gram-negative bacteria associated with early onset periodontitis, including Actinobacillus actinomycetemcomitans and the Capnocytophaga spp. Porcine protegrins showed even greater activity against those organisms, as well as against anaerobic bacteria associated with adult periodontitis, including Porphyromonas gingivalis Prevotella intermedia and Fusobacterium nucleatum. Based on these observations, we believe that protegrin-like β-sheet peptide antibiotics may be useful dental therapeutics.     

Antifungal screening and in silico mechanistic studies of an in‐house azole library

Systemic Candida infections pose a serious public health problem with high morbidity and mortality. C. albicans is the major pathogen identified in candidiasis; however, non‐albicans Candida spp. with antifungal resistance are now more prevalent. Azoles are first‐choice antifungal drugs for candidiasis; however, they are ineffective for certain infections caused by the resistant strains. Azoles block ergosterol synthesis by inhibiting fungal CYP51, which leads to disruption of fungal membrane permeability. In this study, we screened for antifungal activity of an in‐house azole library of 65 compounds to identify hit matter followed by a molecular modeling study for their CYP51 inhibition mechanism. Antifungal susceptibility tests against standard Candida spp. including C. albicans revealed derivatives 12 and 13 as highly active. Furthermore, they showed potent antibiofilm activity as well as neglectable cytotoxicity in a mouse fibroblast assay. According to molecular docking studies, 12 and 13 have the necessary binding characteristics for effective inhibition of CYP51. Finally, molecular dynamics simulations of the C. albicans CYP51 (CACYP51) homology model's catalytic site complexed with 13 were stable demonstrating excellent binding.