Impact of the changing epidemiology of fungal infections in the 1990s

Polysaccharides and lipoproteins as reactants for the synthesis of pharmaceutically important scaffolds: A review

The growing number of diseases in the past decade has once again highlighted the need for extensive research on the development of novel drugs. There has been a major expansion in the number of people suffering from malignant diseases and types of life-threatening microbial infections. The high mortality rates caused by such infections, their associated toxicity, and a growing number of microbes with acquired resistance necessitate the need to further explore and develop the synthesis of pharmaceutically important scaffolds. Chemical entities derived from biological macromolecules like carbohydrates and lipids have been explored and observed to be effective agents in the treatment of microbial infections and diseases. These biological macromolecules offer a variety of chemical properties that have been exploited for the synthesis of pharmaceutically relevant scaffolds. All biological macromolecules are long chains of similar atomic groups which are connected by covalent bonds. By altering the attached groups, the physical and chemical properties can be altered and molded as per the clinical applications and needs, this ring them potential candidates for drug synthesis. The present review establishes the role and significance of biological macromolecules by articulating various reactions and pathways reported in the literature.

Understanding Human Microbiota Offers Novel and Promising Therapeutic Options against Candida Infections

Human fungal pathogens particularly of Candida species are one of the major causes of hospital acquired infections in immunocompromised patients. The limited arsenal of antifungal drugs to treat Candida infections with concomitant evolution of multidrug resistant strains further complicates the management of these infections. Therefore, deployment of novel strategies to surmount the Candida infections requires immediate attention. The human body is a dynamic ecosystem having microbiota usually involving symbionts that benefit from the host, but in turn may act as commensal organisms or affect positively (mutualism) or negatively (pathogenic) the physiology and nourishment of the host. The composition of human microbiota has garnered a lot of recent attention, and despite the common occurrence of Candida spp. within the microbiota, there is still an incomplete picture of relationships between Candida spp. and other microorganism, as well as how such associations are governed. These relationships could be important to have a more holistic understanding of the human microbiota and its connection to Candida infections. Understanding the mechanisms behind commensalism and pathogenesis is vital for the development of efficient therapeutic strategies for these Candida infections. The concept of host-microbiota crosstalk plays critical roles in human health and microbiota dysbiosis and is responsible for various pathologies. Through this review, we attempted to analyze the types of human microbiota and provide an update on the current understanding in the context of health and Candida infections. The information in this article will help as a resource for development of targeted microbial therapies such as pre-/pro-biotics and microbiota transplant that has gained advantage in recent times over antibiotics and established as novel therapeutic strategy.

Aspergillosis, Avian Species and the One Health Perspective: The Possible Importance of Birds in Azole Resistance

The One Health context considers health based on three pillars: humans, animals, and environment. This approach is a strong ally in the surveillance of infectious diseases and in the development of prevention strategies. Aspergillus spp. are fungi that fit substantially in this context, in view of their ubiquity, as well as their importance as plant pathogens, and potentially fatal pathogens for, particularly, humans and avian species. In addition, the emergence of azole resistance, mainly in Aspergillus fumigatus sensu stricto, and the proven role of fungicides widely used on crops, reinforces the need for a multidisciplinary approach to this problem. Avian species are involved in short and long distance travel between different types of landscapes, such as agricultural fields, natural environments and urban environments. Thus, birds can play an important role in the dispersion of Aspergillus, and of special concern, azole-resistant strains. In addition, some bird species are particularly susceptible to aspergillosis. Therefore, avian aspergillosis could be considered as an environmental health indicator. In this review, aspergillosis in humans and birds will be discussed, with focus on the presence of Aspergillus in the environment. We will relate these issues with the emergence of azole resistance on Aspergillus. These topics will be therefore considered and reviewed from the “One Health” perspective.

Nanoparticle-Based Mycosis Vaccine

Many diseases that were considered major affliction of mankind in the past have been successfully eradicated with introduction of appropriate vaccine strategies. In order to expedite new challenges coming up to deal with various infectious diseases, nano-particulate-based subunit vaccines seem to be the demand of ordeal. The nano-vaccines can find better scope for the diseases that were not rampant in the semi-advanced world few years back. For example in present-day circumstances that corroborate with advancement in the field of medical sciences in terms of cancer chemotherapy, organ transplantation, therapy of autoimmune diseases, etc.; along with prevalence of altogether unheard diseases such as HIV infection, people are at risk of infliction with many more pathogens. In this regard, development of an effective prophylactic strategy against many opportunistic infections primarily caused by fungal pathogens needs better understanding of host pathogen relation and role of active immunity against pathogenic fungi. In the present study, we have tried to decipher effectiveness of a nano-sized vaccine delivery system in imparting protection against fungal pathogens.

Genotypes and virulence factors of Candida species isolated from oralcavities of patients with type 2 diabetes mellitus

BACKGROUND/AIM

This study compared the genotypes and virulence factors of Candida species isolated from oral cavities of healthy individuals and patients with diabetes mellitus (DM).

MATERIALS AND METHODS

A total of 142 healthy individuals and 73 diabetic patients participated in this study. Study populations were classified into 4 groups as follows: Group I - Healthy, without caries; Group II - Healthy, with caries; Group III - DM, with caries; Group IV - DM, without caries. Diabetic patients' blood glucose and hemoglobin A1c concentrations were determined. Identification of Candida species was performed with conventional methods. Biofilm production, proteinase, phospholipase, and esterase were analyzed. The genetic diversity of Candida species was established using rep-PCR.

RESULTS

The most isolated species was Candida albicans. There were statistical differences in terms of isolated Candida frequency between healthy subjects and diabetic patients. There was no statistical difference between the virulence factors of groups. Twelve genotypes were determined. While there were statistical differences in aerobe biofilm production, proteinase, and phospholipase activity between genotypes, there were no statistical differences in anaerobe biofilm production and esterase activity between genotypes.

CONCLUSION

Diabetes has no effect on the activities of virulence factors of Candida species. Different genotypes of Candida albicans exhibited different virulence activities.

Profile of yeasts isolated from urinary tracts of catheterized patients

PURPOSE

Nosocomial fungal infections are important cause of morbidity and mortality in hospital patients. Urinary catheters have been held responsible to cause a large number of hospital acquired Urinary Tract Infections (UTIs). This study was undertaken to determine the incidence of nosocomial Candiduria associated with in dwelling urinary catheters, to characterize the species and assess their resistance to antifungal agents.

MATERIALS & METHODS

Urine specimens from 510 catheterized patients were inoculated on Sabauraud Dextrose Agar; the species identification of Candida isolates was done by biochemical tests and antifungal susceptibility testing was done by disc diffusion method.

RESULTS

Candida was isolated in 112 (21.96%) specimens. Of these, Candida albicans was commonly isolated in 50.89% followed by C. tropicalis, C. glabrata, C. krusei, C. parapsilosis, C. guillermondi and C. pseudotropicalis. Fluconazole resistance was encountered in some isolates. All C. glabrata and C. krusei were uniformly resistant to fluconazole and 8 of 16 C. tropicalis were also resistant to it. But only 7 of 57 isolates of C. albicans were resistant to it. Resistance to Nystatin was seen in 34 isolates. Similarly, emergence of resistance was also seen to Ketoconazole and Itraconazole in 24 of 112 isolates. Amphoterecin B resistance was exhibited by 3 C. albicans, 2 C. tropicalis, 1 C. glabrata and 1 C. krusei strain. C. albicans is an important nosocomial pathogen causing UTI in catheterized patients, nevertheless role of other species of Candida as emergent pathogens and resistance to antifungal drugs needs to be emphasized.

Epidemiology of infections in cancer patients

Although major advances in the care of cancer patients over the past several decades have resulted in improved survival, infectious complications remain a significant cause of morbidity and mortality. To successfully identify, treat, and prevent infections, a comprehensive understanding of risk factors that predispose to infection and of commonly encountered pathogens is necessary. In addition, clinicians must keep abreast of the changing epidemiology of infections in this population. As therapeutic modalities continue to evolve, as established pathogens become increasingly drug resistant, and as new pathogens are discovered, successful management of infections will continue to present challenges in the years to come.

Nephrotoxicity and other adverse events among inpatients receiving liposomal amphotericin B or amphotericin B lipid complex

Nephrotoxicity evaluations between liposomal amphotericin B (L-AMB) and amphotericin B lipid complex (ABLC) have provided mixed results. This retrospective study used an electronic medical record database of hospitalized patients with invasive fungal infections treated with either L-AMB or ABLC. Patients had renal insufficiency, clinical condition suggesting intolerance to amphotericin B deoxycholate (CAB), or recent CAB exposure. Baseline SCr, exposure to other nephrotoxic agents, and total amphotericin B exposure were similar between the groups. In 105 patients administered L-AMB, 10.6% had nephrotoxicity versus 22.6% of 222 patients administered ABLC (P = 0.020). A logistic regression model found ABLC patients had 3.48 higher odds (95% CI 1.05-11.52) than L-AMB of developing nephrotoxicity. Infusion reactions were more prevalent with ABLC (23.9% versus 9.5%, P = 0.002) as was hypomagnesemia (44.3% versus 28.1%, P = 0.033). This study demonstrated that L-AMB is associated with less nephrotoxicity, infusion reactions and hypomagnesemia than ABLC in patients at increased risk of nephrotoxicity.

Effect of Amphotericin B Alone or in Combination with Rifampicin or Clarithromycin Against Candida Species Biofilms

Effectiveness of amphotericin B alone or in combination with rifampicin or clarithromycin on the killing of Candida species biofilms was investigated in vitro. Amphotericin B was assayed at 0.005 to 10 mg/ml. Rifampin and clarithromycin were assayed at 10 mg/ml. We studied 7 Candida albicans, 3 Candida parapsilosis, 3 Candida glabrata, 3 Candida krusei and 2 Candida tropicalis strains. Biofilms were developed in 96-well, flat-bottomed microtiter plates for 48 hours. A synergistic effect between amphotericin B and clarithromycin was demonstrated against 66.6% of C. parapsilosis, 66.6% of C. glabrata, and 42.8% of C. albicans biofilms. A synergistic effect between amphotericin B and rifampin was demonstrated against 66.6% of C. parapsilosis, 42.8% of C. albicans, and 33.3% of C. glabrata biofilms. No synergistic effect was observed against C. krusei or C. tropicalis biofilms with any of the combinations. Rifampin or clarithromycin alone did not exert any effect on Candida species biofilms. Rifampin or clarithromycin combinations with amphotericin B might be of interest in the treatment of Candida biofilm-related infections.

Incidence and predictors of invasive candidiasis associated with candidaemia in children

Risk factors for invasive candidiasis in children with candidaemia are poorly defined. We performed a retrospective cohort study of all children with candidaemia at our tertiary children's hospital from 2000 to 2006. Invasive candidiasis was diagnosed by review of the medical record and standardised EORTC/MSG criteria. A variety of risk factors for invasive candidiasis were explored. Of 194 episodes of candidaemia in the microbiology laboratory database, 180 clinical records were available. Evaluation for invasive candidiasis consisted of 174 (97%) echocardiograms, 167 (93%) dilated ophthalmological examinations, 136 (76%) chest CT scans and 108 (60%) abdominal ultrasounds (complete, hepatosplenic or renal). Of the 180 patients, 15 (8%) were identified with invasive candidiasis (4 proven, 1 probable, 10 possible). Prematurity <32 weeks (P < 0.01), an underlying immunocompromising disorder (P < 0.01), and ≥2 days of candidaemia (P = 0.05) were significantly associated with invasive candidiasis. Invasive candidiasis, especially proven or probable, in the setting of candidaemia was not common in our hospital, but premature infants and immunocompromised children were at significantly higher risk. Based on our findings, extensive imaging and examination by an ophthalmologist were particularly low-yield for invasive candidiasis in immunocompetent children beyond infancy.

Effect of Ethiopian multiflora honey on fluconazole-resistant Candida species isolated from the oral cavity of AIDS patients

This study aimed to determine the antifungal effect of Ethiopian multiflora honey against Candida species isolated from the oral cavity of AIDS patients. Oral rinses were obtained from 13 AIDS patients and cultured on CHROMagar plates at 37°C for 48 hours. Candida species were identified by microbiological and molecular techniques. The antifungal effect of the honey sample on Candida was investigated by an agar dilution technique. Susceptibility of the Candida species to fluconazole was tested following a semi-modified microdilution method. Growth of both fluconazole-susceptible and -resistant Candida species was inhibited with a minimum fungicidal concentration (MFC) of 35–40% (v/v) honey. The MFC of different Candida species was not significantly different ( P > 0.05). From the total of 25 Candida isolates tested for susceptibility, 11 (44%), eight (32%) and six (24%) of the isolates were sensitive (minimum inhibitory concentrations [MICs] < 8 µg/mL), susceptible (dose-dependent: MICs 16–32 µg/mL) and resistant (MICs > 64 µg/mL) to fluconazole, respectively. Ethiopian multiflora honey has antifungal activity against fluconazole-resistant Candida species isolated from the oral cavity of AIDS patients. This supports the existing folkloric practice of using honey to treat oral lesions. Nevertheless, identification of the bioactive agents in honey, their clinical evaluation and pharmacological standardization are crucial.

Use of a new gelling agent (Eladium©) as an alternative to agar-agar and its adaptation to screen biofilm-forming yeasts

The incidence of yeast-induced infections has increased in the last decade, mainly because of the increasing number of immunodeficient patients. Since biofilm production is believed to be responsible for fungal virulence, we propose screening yeasts of various genera in order to determine their ability to form biofilms. This is an important issue because yeast cells that form biofilms are particularly resistant to anti-fungal agents used in human patients. For screening, we used Eladium©, a new polysaccharide produced by a Rhizobium sp., as an alternative gelling agent to agar. We also established the conditions necessary to detect biofilm formation. The adapted medium provides the missing link between liquid and solid media. Its advantages include enhancement of growth of microorganisms and facilitation of quick and easy monitoring of biofilm formation.

Epidemiological shifts in opportunistic and nosocomial Candida infections: mycological aspects

Increases in the prevalence of yeast species other than C. albicans as agents of disseminated mycoses in immunosuppressed patients and of fluconazole-resistant C. albicans isolates from patients infected with HIV indicate changes in the epidemiology of Candida infections. The precise reasons for alterations in prevalence of various agents are difficult to pinpoint but changes in the types of host populations at risk of Candida infection and selection of resistant yeast populations by widescale usage of certain antifungal agents seem to be factors involved in the process. Greater attention to speciation of clinical yeasts and standardized susceptibility test methods are needed for future epidemiological surveillance.

Potential use of liposomal diallyl sulfide in the treatment of experimental murine candidiasis

In the present study, we evaluated the potential of a liposomal formulation of the garlic oil component DAS (diallyl sulfide) in treating disseminated infection caused by the intracellular opportunistic pathogen Candida albicans in experimental mice. The PC (phosphatidylcholine) liposomal formulation of DAS was evaluated for size, ζ-potential, entrapment efficiency and release kinetics, toxicity etc. For therapeutic studies, mice were challenged with intravenous infection dosage of 107 blastospores of C. albicans followed by treatment with various doses of DAS formulations [12 and 6 mg/kg b.w. (body mass)] three times, on alternative days. The antifungal efficacy of liposomal DAS was assessed on the basis of survival of treated mice as well as the residual fungal load in vital organs like liver and spleen of mice. The results of the present study showed that treatment with DAS-bearing liposomes (12 mg/kg b.w.) resulted in the highest survival rate in animals. Liposomal DAS also significantly decreased residual fungal load in vital organs of experimental animals compared with the free form of DAS. The liposomal DAS was also found to be free of toxic manifestations as revealed by the erythrocyte lysis test and liver/kidney function tests. The results of the present study established that the antifungal activity of DAS, a poorly soluble compound, can be enhanced by the incorporation of it into liposomes. Further studies and optimizations are needed to build upon the promising findings of this study to enable the development of an effective plant-derived antifungal formulation that can provide an alternative to currently available antifungal drugs.

Sequence-based identification of filamentous basidiomycetous fungi from clinical specimens: a cautionary note

The species-level identification of sterile and/or arthroconidium-forming filamentous fungi presumed to be basidiomycetes based upon morphological or physiological features alone is usually not possible due to the limited amount of hyphal differentiation. Therefore, a reliable molecular approach capable of the unambiguous identification of clinical isolates is needed. One hundred sixty-eight presumptive basidiomycetes were screened by sequence analysis of the internal transcribed spacer (ITS) and D1/D2 ribosomal DNA regions in an effort to obtain a species identification. Through the use of this approach, identification of a basidiomycetous fungus to the species level was obtained for 167/168 of the isolates. However, comparison of the BLAST results for each isolate for both regions revealed that only 28.6% (48/168) of the isolates had the same species identification by use of both the ITS and the D1/D2 regions, regardless of the percent identity. At the less stringent genus-only level, the identities for only 48.8% (82/168) of the isolates agreed for both regions. Investigation of the causes for this low level of agreement revealed that 14% of the species lacked an ITS region deposit and 16% lacked a D1/D2 region deposit. Few GenBank deposits were found to be complete for either region, with only 8% of the isolates having a complete ITS region and 10% having a complete D1/D2 region. This study demonstrates that while sequence-based identification is a powerful tool for many fungi, sequence data derived from filamentous basidiomycetes should be interpreted carefully, particularly in the context of missing or incomplete GenBank data, and, whenever possible, should be evaluated in light of compatible morphological features.

Efficacy of niosomal formulation of diallyl sulfide against experimental candidiasis in Swiss albino mice

Aim: We developed a niosomal formulation of diallyl sulfide (DAS), a garlic oil component, and evaluated its efficacy against experimental candidiasis in mice. Methods: DAS-bearing niosomes prepared from sorbitan monoester surfactants were evaluated for drug entrapment efficiency, release kinetics, toxicity, size, ζ-potential and others. Mice challenged with Candida albicans were treated with various DAS formulations. The efficacy of the formulations was assessed on the basis of reduction in mortality and decrease in residual fungal load in vital organs, such as liver and spleen, of treated mice. Results: Niosomal DAS (12 mg/kg body weight) significantly reduced fungal load and mortality in treated animals compared with the free form of DAS. Niosomal DAS was also found to be free of toxic manifestations, as revealed by histopathological studies, as well as liver/kidney function tests. Conclusion: Incorporation of DAS in niosomes enhances its antifungal efficacy. Further studies are needed to optimize the current findings to develop an efficient nature-derived alternative antifungal therapeutic strategy.

Stereoselective synthesis and antimicrobial activity of benzofuran-based (1E)-1-(piperidin-1-yl)-N2-arylamidrazones

The reaction of 2-oxo-N-arylpropanehydrazonoyl chlorides 3a-e with 3-methyl-2-benzofurancarboxylic acid hydrazide (7) furnished N-(aryl)propanehydrazonoyl chlorides 8a-e. X-Ray of 8c revealed the (1Z,2E) configuration of structure 8. Nucleophilic substitution reaction of 8a or 8d with piperidine resulted in the formation of 1-(piperidin-1-yl)-N(2)-arylamidrazones 9a, b. The X-ray diffraction of 9b showed its (1E,2E) configuration and it confirmed the stereoselectivity of the latter reaction. (1E,2Z,3E)-1-(Piperidin-1-yl)-1-(arylhydrazono)-2-[(3-methylbenzofuran-2-oyl)hydrazono]-4-arylbut-3-enes 11 were synthesized in stereoselective reaction from 8 or alternatively from 9. X-ray analysis of 11b showed a conversion of configuration respect to 8d or 9b. X-Ray analysis of 9b and 11b revealed the role of hydrogen interactions in the stereochemistry of their solid state structure. The in vitro antimicrobial activity of the newly synthesized compounds demonstrated an excellent growth inhibition of compounds 9 and 11 against clinically isolated strains of human fungal pathogens and exhibited a significant potency against gram-positive bacteria. Griseofulvin and Amoxicilline were used as references for antifungal and antibacterial screening. The effect of most potent antifungal compound 9b on morphological features of Aspergillus fumigatus and Candida albicans using image analyzer was studied. Furthermore, the effect of 9b on the ultra-structures of the latter fungi was occurred by transmission electron microscope.

Strategies developed by bacteria and virus for protection from the human complement system

The complement system is an important part of innate immunity providing immediate protection against pathogens without a need for previous exposure. Its importance is clearly shown by the fact that patients lacking complement components suffer from fulminant and recurring infections. Complement is an explosive cascade, and in order to control it there are inhibitors present on every human cell and also circulating in blood. However, many infectious agents have developed strategies to prevent clearance and destruction by complement. Some pathogens simply hijack the host's complement inhibitors, while others are able to produce their own homologues of human inhibitors. Knowledge of these mechanisms on a molecular level may aid development of vaccines and novel therapeutic strategies that would be more specific than the use of antibiotics that, apart from causing resistance problems, also affect the normal flora, the outcome of which could be devastating. In this study the structural requirements and functional consequences of interactions between the major soluble inhibitor of complement C4b-binding protein and Neisseria gonorrhoeae, Bordetella pertussis, Streptococcus pyogenes, Escherichia coli K1, Moraxella catarrhalis and Candida albicans are described. Furthermore, a novel inhibitor produced by Kaposi's sarcoma-associated herpesvirus is identified and characterized in detail: KCP. It is shown that KCP inhibits classical C3-convertase and presents activated complement factors C4b and C3b for destruction by a serine proteinase, factor I. Using molecular modelling and site-directed mutagenesis, it was possible to localize sites on the surface of KCP required for complement inhibition and it is concluded that KCP uses molecular mechanisms identical to human inhibitors.

Complement evasion strategies of pathogens-acquisition of inhibitors and beyond

Activation of the complement system and resulting opsonisation with C3b are key events of the innate immune defense against infections. However, a wide variety of bacterial pathogens subvert complement attack by binding host complement inhibitors such as C4b-binding protein, factor H and vitronectin, which results in diminished opsonophagocytosis and killing of bacteria by lysis. Another widely used strategy is production of proteases, which can effectively degrade crucial complement components. Furthermore, bacterial pathogens such as Moraxella catarrhalis and Staphylococcus aureus capture and incapacitate the key complement component C3. The current review describes examples of these three strategies. Targeting binding sites for complement inhibitors on bacterial surfaces and complement-degrading proteases with vaccine-induced antibodies may be used to enhance a common vaccine design strategy that depends on the generation of complement-dependent bactericidal and opsonophagocytic antibody activities.

Contribution of interactions between complement inhibitor C4b-binding protein and pathogens to their ability to establish infection with particular emphasis on Neisseria gonorrhoeae

Complement activation and resulting opsonisation with C3b form key arms of the innate immune defense against infections. However, a wide variety of pathogens subvert complement attack by binding host complement inhibitors, which results in diminished opsonophagocytosis and killing of bacteria by lysis. Human C4b-binding protein (C4BP) binds Neisseria gonorrhoeae and Streptococcus pyogenes, both uniquely human pathogens. This binding specificity is circumvented by other bacterial species, which bind C4BP from numerous mammalian hosts that they infect. Binding of C4BP to Neisseria is mediated by outer membrane porin proteins and appears to be one of the main factors mediating serum resistance. Targeting C4BP binding sites on bacterial surfaces with vaccine-induced antibodies may block binding of C4BP and enhance a common vaccine design strategy that depends on the generation of complement-dependent bactericidal and opsonophagocytic antibody activities.

[Hepatosplenic candidiasis in acute leukaemia patients]

INTRODUCTION

Hepatosplenic candidiasis is a disseminated invasive fungal infection that may affects patients with acute leukaemia. The main clinical manifestation is a persistent fever in patients recovered from prolonged neutropenia after recent chemotherapy.

CASE OUTLINE

The authors present three patients, two women and one men, aged 23, 26 and 33 years, with acute leukaemia; one with acute myeloblastic and two with acute lymphoblastic leukaemia who developed hepatosplenic candidiasis. The diagnosis was based on prolonged fever, elevated serum bilirubin and alkaline phosphatase, as well as characteristic lesions on computed tomography, nuclear magnetic resonance and ultrasonographic findings and positive blood culture in one patient. The antifungal treatment was successful in one patient only. Two patients died due to progression of leukaemia.

CONCLUSION

If leukaemia patient in remission after chemotherapy develops a prolonged fever of unknown origin, hepatosplenic candidiasis has to be considered and all efforts should be done to diagnose it. The diagnosis is based on clinical presentation and imaging techniques. The positive cultures of fungi are not usually possible and are not mandatory. The antifungal treatment may be prolonged, sometimes 2 to 3 months or even more.

Complement evasion of pathogens: common strategies are shared by diverse organisms

Infectious diseases represent a major health problem. Based on the limited efficacy of existing drugs and vaccines and the increasing antibiotic resistance new strategies are needed to fight infectious diseases. A better understanding of pathogen-host interaction is one important aspect to identify new virulence factors and antimicrobial and anti-inflammatory compounds utilized by pathogens represent an additional source for effective anti-inflammatory compounds. Complement forms a major defense line against invading microbes, and pathogens have learned during evolution to breach this defense line. The characterization of how pathogens evade complement attack is a rapidly developing field of current research. Pathogens mimic host surfaces and bind host complement regulators. Similarly pathogens utilize a number of complement inhibitory molecules which help to evade complement attack and which display anti-inflammatory activity. The molecular identification of these molecules, as well as the functional characterization of their roles at the pathogen-host interface is an important and emerging field of infection biology. In addition, pathogens utilize multiple sets of such regulators as redundancy and multiplicity is important for immune and complement evasion. Here we summarize the current scenarios of this emerging field which identifies multiple virulence factors and complement evasion strategies, but which at the same time reveals common mechanisms for immune and complement defense.

Gpm1p is a factor H-, FHL-1-, and plasminogen-binding surface protein of Candida albicans

The human pathogenic yeast Candida albicans utilizes host complement regulators for immune evasion. Here we identify the first fungal protein that binds Factor H and FHL-1. By screening a protein array of 4088 proteins of Saccharomyces cerevisiae, phosphoglycerate mutase (ScGpm1p) was identified as a Factor H- and FHL-1-binding protein. The homologous C. albicans Gpm1p (CaGpm1p) was cloned and recombinantly expressed as a 36-kDa His-tagged protein. Purified CaGpm1p binds the host complement regulators Factor H and FHL-1, but not C4BP. The CaGpm1p binding regions in the host proteins were localized; FHL-1 binds via short consensus repeats (SCRs) 6 and 7, and Factor H utilizes two contact regions that are located in SCRs 6 and 7 and in SCRs 19 and 20. In addition, recombinant CaGpm1p binds plasminogen via lysine residues. CaGpm1p is a surface protein as demonstrated by immunostaining and flow cytometry. A C. albicans gpm1(-/-) mutant strain was generated that did not grow on glucose-supplemented but on ethanol- and glycerol-supplemented medium. Reduced binding of Factor H and plasminogen to the null mutant strain is in agreement with the presence of additional binding proteins. Attached to CaGpm1p, each of the three host plasma proteins is functionally active. Factor H and FHL-1 show cofactor activity for cleavage of C3b, and bound plasminogen is converted by urokinase-type plasminogen activator to proteolytically active plasmin. Thus, the surface-expressed CaGpm1p is a virulence factor that utilizes the host Factor H, FHL-1, and plasminogen for immune evasion and degradation of extracellular matrices.

Genomics and the development of new diagnostics and anti-Candida drugs

Pathogenic Candida species remain a significant medical problem despite the availability of antifungal therapies. Two key issues must be addressed to improve the treatment of life-threatening systemic Candida infections. First, advanced diagnostic tools are required to facilitate the early identification of these infections, when therapeutic intervention is more likely to be effective. Second, improved antifungal therapies are needed. These therapies, which might include combinations of antifungals, need to be less toxic to the patient and more potent in killing a broader range of Candida species. Recent advances in unravelling the genomics of these species should facilitate efforts to achieve these goals. We discuss the contribution of genomics to the development of novel antifungals and new diagnostic tools.

A possible CD1a Langerhans cell-mast cell interaction in chronic hyperplastic candidosis

AIMS

T lymphocyte-antigen-presenting cell (APC) interaction plays a central role in T lymphocyte activation and APC maturation. We therefore studied the CD1a-positive Langerhans cells with respect to receptor activator of nuclear factor kappa B ligand (RANKL)-positive cells in chronic hyperplastic candidosis (CHC).

MATERIALS AND METHODS

Tissue sections of CHC were compared with leukoplakia and healthy oral mucosa using RANKL and CD1a monoclonal antibodies in an avidin-biotin peroxidase complex protocol. Two different antigen-retrieval protocols, pepsin preincubation and Tris-EDTA heat treatment, were used.

RESULTS

CD1a-positive Langerhans cells were in healthy and leukoplakia epithelium found in the middle layer, but in CHC in all layers of the epithelium, at the basement membrane and as mononuclear round cells in the lamina propria. Use of pepsin digestion enabled studies of mast cells and their activation in the form of degranulation of RANKL.

CONCLUSIONS

The numerical, morphological and topographical versatility of the CD1a-positive Langerhans cells in CHC can be clarified by dendritic cell (DC) recruitment into the epithelium. RANK-positive and RANKL-sensitive DCs have ample opportunity to interact with local T lymphocytes. Use of an optimized antigen-retrieval protocol enabled demonstration of an active engagement (degranulation) of mast cells, which represent a rapidly available source of soluble RANKL.

Attributable mortality of candidemia: a systematic review of matched cohort and case-control studies

A systematic review of matched cohort and case-control studies was performed to examine the mortality attributable to candidemia. The review included studies that compared mortality of patients with candidemia (cases) to that of matched patients without candidemia (controls). Secondary variables examined were the length and cost of hospital stay. Relevant studies were identified using the PubMed database and by examining the references of the initially selected studies. Two independent reviewers performed the literature search, study selection and data extraction from the identified studies. A total of seven studies were included in the review. The patients included those hospitalized in intensive care units (ICU) and hospital wards and those undergoing transplantation. The mortality attributed to candidemia in the reviewed studies ranged from 5 to 71%. For six of the reviewed studies the difference in mortality between cases and controls was statistically significant. Among those who survived, the length of stay and the cost of hospitalization of patients with candidemia were significantly higher than those of controls. Despite the methodological heterogeneity of the reviewed studies, the data from the available matched cohort and case-control studies suggest that candidemia is associated with considerable mortality that is attributed, at least to some degree, to the infection itself and not only to the presence of another comorbidity.

Detección y caracterización cinética de una contaminación por Candida tropicalis durante la producción de levadura forrajera

Candida tropicalis was identified as the etiologic agent of a severe contamination detected on an industrial fodder yeast production at the Cuban eastern region. After a detailed diagnostic task on raw material carried out on different factory sections, protocols to identify the contamination source and to isolate the microorganism were proposed. The identification was by comparison of the internal transcribed spacers ITS1 and ITS4 from 5.8S ribosomal DNA nucleotide sequences. In parallel, propagation of production strain, Candida utilis NRRL Y-660, at lab scale (2.5 l) was performed. Similar results to those observed in the factory concerning to its kinetic behavior in aerobic propagation with contaminated molasses, were detected at this level. The identification and primary kinetic characterization led to the implementation of sanitary and technological measures to bring production at its normal operational conditions as well as the application of prophylactic surveillance methodologies to avoid future contaminations.

Management of invasive candidiasis in critically ill patients

Candida species have become predominant pathogens in critically ill patients. In this population, invasive candidiasis is associated with a poor prognosis but adequate management can limit the attributable mortality. Adequate management, however, is hampered by a problematic diagnosis as the clinical picture of invasive disease is non-specific and blood cultures have a low sensitivity. Moreover, it is often hard to differentiate colonisation from infection and many critically ill patients are heavily colonised with Candida species, especially when receiving broad-spectrum antibacterials. The question of which antifungal agent to choose has become more complex as the development of new drugs raises promising expectations. Until the 1980s therapy for invasive candidiasis was limited to amphotericin B, but with the advent of new antifungal agents, such as azoles and echinocandins, less toxic therapeutic options are possible and doors have opened towards prevention and optimised therapy in the case of documented candidiasis. Through the arrival of these new antifungal agents, a range of therapeutic strategies for the management of invasive candidiasis has been developed: antifungal prophylaxis, pre-emptive therapy, and empirical and definitive antifungal therapy. Each of these strategies has a specific target population, as defined by specific underlying conditions and/or individual risk factors. Antifungal prophylaxis, in order to prevent candidal infection, is based on the type of underlying diseases with a high risk for invasive candidiasis. Individual risk factors are not taken into account. Potential indications are bone marrow transplantation, liver transplantation, recurrent gastrointestinal perforations or leakages, and surgery for acute necrotising pancreatitis. Pre-emptive therapy is also a preventive strategy. It can be recommended on the basis of an individual risk profile including overt candidal colonisation. Empirical therapy is started in patients with a risk profile for invasive candidiasis. It is recommended in the presence of clinical signs of infection, deteriorating clinical parameters, or a clinical picture of infection not responding to antibacterials but in the absence of a clear causative pathogen. Definitive antifungal therapy is defined as therapy in patients with documented invasive infection. The main goal is to maintain a balance between optimal prevention and timely initiation of therapy on one hand, and to minimise selection pressure in order to avoid a shift towards less susceptible Candida species on the other hand.

Antimycotic Drug Discovery in the Age of Genomics

Genomic-based methodologies are increasingly used at all stages of drug development. The most extensive applications have occurred in early drug discovery stages due to advances in technologies that allow for automated synthesis and characterization of organic compounds, and for high-throughput screening of these molecules against known drug targets. The adaptation of genomic-based methodologies in later stages of drug development presents a more difficult task. In this review we describe how genomics can be used to identify previously uncharacterized pharmacologic actions that provide a basis for the development of new classes of antimycotic agents or for adverse event aversion. Clinically, novel antimycotics are gravely needed. This review provides a perspective on new technologies that will bridge the gap between drug discovery and development that may enable more rapid access to new antimycotic agents.

The hyphal and yeast forms of Candida albicans bind the complement regulator C4b-binding protein

Candida albicans, an important pathogenic yeast, activates all three pathways of the complement system. To understand how this yeast evades the effects of the activated system, we have analyzed the binding of the classical pathway inhibitor C4b-binding protein (C4BP) by C. albicans. Purified native as well as recombinant C4BP bound dose dependently to the yeast and hyphal forms, as shown by multiple methods, such as confocal microscopy, flow cytometry, a novel enzyme-linked immunosorbent assay, absorption from human serum, and direct binding assays with purified proteins. A prominent binding site was identified at the tip of the germ tube, a structure that is considered important for tissue penetration and pathogenesis. The binding site in C4BP was localized to the two N-terminal complement control protein domains by using recombinant deletion constructs and site-specific monoclonal antibodies. As the alternative pathway inhibitors factor H and FHL-1 also bind to C. albicans, the binding of all three plasma proteins was compared. Simultaneous binding of the classical regulator C4BP and the alternative pathway regulator factor H was demonstrated by confocal microscopy. In addition, FHL-1 competed for binding with C4BP, suggesting that these two related complement regulators bind to the same structures on the yeast surface. The surface-attached C4BP maintains its complement regulatory activities and inactivates C4b. The surface-attached human C4BP serves multiple functions relevant for immune evasion and likely pathogenicity. It inhibits complement activation at the yeast surface and, in addition, mediates adhesion of C. albicans to host endothelial cells.

Complement inhibitor C4b-binding protein-friend or foe in the innate immune system?

The complement system constitutes an important component of the defence against foreign organisms, functioning both in innate and adaptive immune systems. It is potentially harmful also to the own organism and is therefore tightly regulated by a number of membrane-bound and soluble factors. C4b-binding protein (C4BP) is a potent circulating soluble inhibitor of the classical and lectin pathways of complement. In recent years, the relationships between the structure of C4BP and its functions have been elucidated using a combination of computer-based molecular analysis and recombinant DNA technologies. Moreover, two novel functions have recently been ascribed to C4BP. One is the ability of C4BP to localize complement regulatory activity to the surface of apoptotic cells via its interaction with the membrane-binding vitamin K-dependent protein S. The other is the ability of C4BP to act as a survival factor for B cells due to an interaction with CD40. The complement regulatory activity of C4BP is not only beneficial because it is also explored by pathogens such as Neisseria gonorrhoeae, Bordetella pertussis, Streptococcus pyogenes, Escherichia coli K1, and Candida albicans, that bind C4BP to their surfaces. This contributes to the serum resistance and the pathogenicity of these bacteria. In this review, the structural requirements and functional importance of the interactions between C4BP and its various ligands are discussed.

Mannich reaction: an approach for the synthesis of water soluble mulundocandin analogues

Semisynthetic modifications at Hydroxy tyrosine (Htyr) unit of mulundocandin (1) were carried out to improve its aqueous solubility. A single step introduction of substituted aminomethyl groups at the ortho position(s) of phenolic hydroxyl of HTyr unit of mulundocandin has been achieved in 7-85% yield. The in vitro screening of Mannich products against Candida albicans and Aspergillus fumigatus, retained the in vivo activity of parent by oral and intraperitoneal route. Compound 20, showed significant improvement in activity over mulundocandin (1) and activity compares well with that of fluconazole.

Burden of hospitalization of patients with Candida and Aspergillus infections in Australia

OBJECTIVES

This study examined the burden of hospitalization of patients with Aspergillus and Candida infections in Australia from 1995 to 1999.

METHODS

Data were extracted from the National Hospital Morbidity Database. A hospitalization with an aspergillosis diagnosis was defined as any discharge with a diagnosis of aspergillosis. A hospitalization with a candidiasis diagnosis was defined as any discharge with a diagnosis of disseminated, invasive, or non-invasive candidiasis. Outcome measures included number of hospitalizations, length of stay (LOS), cost (AUS$), and mortality.

RESULTS

4583 hospitalizations with an aspergillosis diagnosis and 57,758 hospitalizations with a candidiasis diagnosis were identified. These hospitalizations were associated with a total of 813,398 hospital days, AUS$563 million in cost, and 4967 in-hospital deaths during the study period. The mean LOS for a hospitalization with an aspergillosis diagnosis was 12 days, cost AUS$9,334, and was associated with 8% mortality. For disseminated, invasive, and non-invasive candidiasis, the respective mean LOS were 31, 17, and 12 days; costs were AUS$33,274, AUS$12,954, and AUS$7,694; and mortality was 26%, 9%, and 8%.

CONCLUSIONS

Hospitalizations with diagnoses for fungal infections were associated with lengthy hospital stays, high costs, and high mortality.

Colonization and epithelial adhesion in the pathogenesis of neonatal candidiasis

Candida species are important nosocomial pathogens in the newborn population, particularly among the premature very-low-birth-weight infants in neonatal intensive care units. Candida colonization of the neonatal skin and gastrointestinal tract is an important first step in the pathogenesis of invasive disease. C albicans is the most commonly isolated species in colonized or infected infants. Over the past decade the incidence of both colonization and infection with other Candida species, particularly C parapsilosis, has risen dramatically. Colonization of the infant occurs early in life and is affected by a variety of common practices in neonatal intensive care. Microbial factors also augment colonization, including the ability of Candida to adhere to human epithelium. A better understanding of the complex interactions between host risk factors and virulence traits of colonizing yeast may allow the risk of systemic spread to be reduced in the population of premature infants.

[Fungal colonization and/or infection in intensive care units. Multicenter study of 1,562 patients]

BACKGROUND AND OBJECTIVE

Our objective was to assess the frequency of fungal colonization and/or infection in critically ill patients admitted to intensive care units (ICUs) and to describe the characteristics and risk factors of those patients in whom fungi had been isolated.

PATIENTS AND METHOD

Observational, multicenter study of patients admitted to 64 ICUs on March 23, June 22, and November 16, 1999. In these patients, the presence of fungi was investigated in some biological sample from the day of ICU admission to the day of assessment of fungal infection. Patients were classified as colonized or infected by fungi.

RESULTS

A total of 1,562 patients were included: 686 in the first period, 567 in the second, and 309 in the third, with a mean of 24.4 patients per ICU (range, 9-62). Fungi were isolated in 456 biological samples from 248 patients (15.9 patients per each series of 100 controlled patients): lung in 183 (40.1%) cases, urine in 90 (19.7%) cases, and oropharynx in 46 (10.1%) cases. Fungi were isolated in blood cultures in 17 (3.7%) patients. Candida albicans was the most frequently isolated fungal species in all sites (68.9%). Isolation of fungi allowed a diagnosis of fungal infection in 121 patients (fungal infection rate, 7.7 episodes per 100 patients admitted to the ICU). Individual risk factors for fungal infection were as follows: previous use of antimicrobials (OR=5.01; 95% CI, 1.77-14.2); mechanical ventilation (OR=3.45; 95% CI, 1.61-7.40); urgent surgical procedures (OR = 2.44; 95% CI, 1.59-3.74); solid neoplasm (OR=2.32; 95% CI, 1.29-4.19); use of corticosteroids (OR = 1.88; 95% CI, 1.18-2.99); and APACHE II score (OR=1.05; 95% CI, 1.02-1.07).

CONCLUSIONS

Fungi were isolated in 15.9% patients admitted to ICUs and they were the causative agents of infection in 7.7% of cases. Candida albicans predominated in all sites. Risk factors for fungal infection included previous use of antibiotics, mechanical ventilation, urgent surgery, solid tumor, use of corticosteroids, and intermediate severity of illness according to the APACHE II score.

The impact of polyene, azole, and DNA analogue antimycotics on the cell surface hydrophobicity of Candida albicans and Candida tropicalis in HIV infection

Oral candidiasis is the most common opportunistic infection in individuals infected with the human immunodeficiency virus. Though Candida albicans is the major aetiological agent, non-albicans species such Candida tropicalis are now emerging as important agents of such infection. The Candida cell surface hydrophobicity (CSH) is considered a critical factor contributing to its colonization potential and virulence. It is also known that brief exposure to sub-cidal concentrations of antifungal agents is a likely scenario in the oral environment where the administered drugs are diluted continuously due to the flushing action of saliva. Hence the objective of the present study was to compare the CSH of 10 isolates each of C. albicans and C. tropicalis from HIV-infected individuals following brief exposure (1 hour) of isolates to sub-therapeutic concentrations of nystatin, amphotericin B, ketoconazole, fluconazole and 5-flurocytosine. The CSH was assessed by a previously described biphasic aqueous-hydrocarbon assay. The mean percentage reduction of CSH of C. albicans following brief exposure to nystatin, amphotericin B, ketoconazole, fluconazole and 5-flurocytosine was 27.33 (p < 0.001), 21.34 (p < 0.05), 11.74 (p > 0.05), 18.4 (p > 0.05) and 14.64 (p > 0.05) respectively. The mean percentage reduction of CSH of C. tropicalis following brief exposure to nystatin, amphotericin B, ketoconazole, fluconazole and 5-flurocytosine was 33.81 (p < 0.01), 28.88 (p < 0.01), 12.6 (p > 0.05), 21.53 (p > 0.05) and 17.68 (p > 0.05) respectively. A significant interspecies variation in CSH was observed for nystatin and amphoterecin B. Overall the results reveal that the CSH of C. albicans is affected to a significantly lesser degree compared with C. tropicalis when exposed to the antifungals. These data further illustrate another mode of action of antifungals on Candida leading to a reduction in the CSH and thereby the yeast adherence to host tissues.

Secular trends of candidemia over 12 years in adult patients at a tertiary care hospital

The incidence of fungal infections has been increasing for the last 3 decades, especially among neutropenic, cancer, and critically ill patients. These infections are associated with high mortality rates. We retrospectively reviewed medical charts of adult patients with fungemia from 1989 to 2000 at our institution. The characteristics of the population groups served by the hospital were described. Of 328 patients with fungemia, we reviewed 315 (96%) medical records, and focused on those with candidemia (n = 294). The species distribution in patients with candidemia showed that the most commonly identified species were Candida albicans (66%), followed by C. glabrata (17%), and C. parapsilosis (6%). The incidence of candidemia ranged from 0.2 to 0.46 per 10,000 patient-days with the highest incidence in 1993 and the lowest in 1997. Although most studies show an increased incidence of candidemia, we observed a reduction over the study period. Furthermore, we observed no shift from C. albicans to non-albicans Candida species despite a significant increase in the use of fluconazole. The overall mortality among patients with candidemia was 44%, with the highest rate in patients over 65 years (52%). Factors independently associated with higher mortality were patient age greater than 65 years, intensive care unit admission, and underlying cancer.

Inhibition of Candida albicans biofilm formation by farnesol, a quorum-sensing molecule

Farnesol is a quorum-sensing molecule that inhibits filamentation in Candida albicans. Both filamentation and quorum sensing are deemed to be important factors in C. albicans biofilm development. Here we examined the effect of farnesol on C. albicans biofilm formation. C. albicans adherent cell populations (after 0, 1, 2, and 4 h of adherence) and preformed biofilms (24 h) were treated with various concentrations of farnesol (0, 3, 30, and 300 micro M) and incubated at 37 degrees C for 24 h. The extent and characteristics of biofilm formation were then assessed microscopically and with a semiquantitative colorimetric technique based on the use of 2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide. The results indicated that the effect of farnesol was dependent on the concentration of this compound and the initial adherence time, and preincubation with 300 micro M farnesol completely inhibited biofilm formation. Supernatant media recovered from mature biofilms inhibited the ability of planktonic C. albicans to form filaments, indicating that a morphogenetic autoregulatory compound is produced in situ in biofilms. Northern blot analysis of RNA extracted from cells in biofilms indicated that the levels of expression of HWP1, encoding a hypha-specific wall protein, were decreased in farnesol-treated biofilms compared to the levels in controls. Our results indicate that farnesol acts as a naturally occurring quorum-sensing molecule which inhibits biofilm formation, and we discuss its potential for further development and use as a novel therapeutic agent.