Epidemiology

Klebsiella pneumoniae prevents spore germination and hyphal development of Aspergillus species

Different bacteria and fungi live as commensal organisms as part of the human microbiota, but shifts to a pathogenic state potentially leading to septic infections commonly occur in immunocompromised individuals. Several studies have reported synergistic or antagonistic interactions between individual bacteria and fungi which might be of clinical relevance. Here, we present first evidence for the interaction between Klebsiella pneumoniae and several Aspergillus species including A. fumigatus, A. terreus, A. niger and A. flavus which cohabit in the lungs and the intestines. Microbiological and molecular methods were employed to investigate the interaction in vitro, and the results indicate that Klebsiella pneumoniae is able to prevent Aspergillus spp. spore germination and hyphal development. The inhibitory effect is reversible, as demonstrated by growth recovery of Aspergillus spp. upon inhibition or elimination of the bacteria, and is apparently dependent on the physical interaction with metabolically active bacteria. Molecular analysis of Klebsiella-Aspergillus interaction has shown upregulation of Aspergillus cell wall-related genes and downregulation of hyphae-related genes, suggesting that Klebsiella induces cell wall stress response mechanisms and suppresses filamentous growth. Characterization of polymicrobial interactions may provide the basis for improved clinical management of mixed infections by setting the stage for appropriate diagnostics and ultimately for optimized treatment strategies.

Emerging biopharmaceuticals from marine actinobacteria

Actinobacteria are quotidian microorganisms in the marine world, playing a crucial ecological role in the recycling of refractory biomaterials and producing novel secondary metabolites with pharmaceutical applications. Actinobacteria have been isolated from the huge area of marine organisms including sponges, tunicates, corals, mollusks, crabs, mangroves and seaweeds. Natural products investigation of the marine actinobacteria revealed that they can synthesize numerous natural products including alkaloids, polyketides, peptides, isoprenoids, phenazines, sterols, and others. These natural products have a potential to provide future drugs against crucial diseases like cancer, HIV, microbial and protozoal infections and severe inflammations. Therefore, marine actinobacteria portray as a pivotal resource for marine drugs. It is an upcoming field of research to probe a novel and pharmaceutically important secondary metabolites from marine actinobacteria. In this review, we attempt to summarize the present knowledge on the diversity, chemistry and mechanism of action of marine actinobacteria-derived secondary metabolites from 2007 to 2016.

Biofilm formation by Aspergillus fumigatus

Aspergillus fumigatus is a well adapted, opportunistic fungus that causes a severe and commonly fatal disease, invasive pulmonary aspergillosis (IPA), in highly immunocompromised patients, aspergilloma in patients with lung cavities and allergic bronchopulmonary aspergillosis (ABPA) in hypersensitive individuals. Recent studies have suggested that biofilm formation by A. fumigatus may be one of the most important virulence factors in IPA and aspergilloma. Several fungal constituents may contribute to the formation of biofilm structures on host cells, including cell wall components, secondary metabolites and drug transporters. The biofilm phenotype of the fungus is refractory to most conventional antifungal treatment options. Thus, an in-depth analysis and understanding of A. fumigatus biofilms is necessary to devise newer and better antifungal targets for treating complex A. fumigatus biofilm-associated diseases.

Biogenic nanosilver incorporated reverse osmosis membrane for antibacterial and antifungal activities against selected pathogenic strains: an enhanced eco-friendly water disinfection approach

Reverse osmosis (RO) membranes have been used extensively in water desalination plants, waste water treatment in industries, agricultural farms and drinking water production applications. The objective of this work is to impart antibacterial and antifungal activities to commercially available RO membrane used in water purification systems by incorporating biogenic silver nanoparticles(AgNPs) synthesized using Rosa indica wichuriana hybrid leaf extract. The morphology and surface topography of uncoated and AgNPs-coated RO membrane were studied using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Elemental composition of the AgNPs-coated RO membrane was analyzed by energy-dispersive X-ray spectroscopy (EDAX). The functional groups were identified by Fourier Transform Infrared spectroscopy (FT-IR). Hydrophilicity of the uncoated and AgNPs-coated RO membrane was analyzed using water contact angle measurements. The thermal properties were studied by thermogravimetric analysis (TGA). The AgNPs incorporated RO membrane exhibited good antibacterial and antifungal activities against pathogenic bacterial strains such as E. coli, S. aureus, M. luteus, K. pneumoniae, and P. aeruginosa and fungal strains such as Candida tropicalis, C. krusei, C. glabrata, and C. albicans.

In vitro analyses of mild heat stress in combination with antifungal agents against Aspergillus fumigatus biofilm

Aspergillus fumigatus biofilms still present a challenge for effective treatment in clinical settings. While mild heat stress has been introduced as a treatment for infectious diseases, the effectiveness of mild heat stress on A. fumigatus biofilm formation and antifungal susceptibility is still unknown. In the present study, confocal laser scanning microscopy (CLSM) was used to image and quantify Aspergillus fumigatus biofilm formation under three different regimens of continuous mild heat stress: at 37, 39, and 41°C. Furthermore, fungal growth has been investigated under the above conditions in combination with antifungal drugs (amphotericin B [AMB], micafungin [MCF], and voriconazole [VOC]) at early and late stages. CLSM analysis showed that higher temperatures induce earlier germination and greater hyphal elongation but poorer polar growth and reduced biofilm thickness. In the early stage of biofilm formation, the combination of treatment at 39 or 41°C with MCF or VOC produced no visible difference in biomass formation from similar treatments at 37°C with the same drug. Interestingly, AMB treatment at 37°C inhibited early stage biofilm formation to a much greater extent than at 39 and 41°C. At the late stage of biofilm formation, the mild heat treatments at 39 and 41°C with AMB, MCF, and VOC inhibited biomass formation compared to that at 37°C. The present data show that mild heat stress has a negative regulatory effect on biofilm formation in vitro, and antifungal drug improvement with mild heat treatment at late-stage biofilm formation provides useful indications of possible effective strategies for clinical management of aspergillosis.

A novel polyamide SL-A92 as a potential fungal resistance blocker: synthesis and bioactivities in Candida albicans

AIM

To synthesize a novel polyamide SL-A92 and evaluate its bioactivity against drug resistance in Candida albicans.

METHODS

SL-A92 was synthesized using N-hydroxybenzotriazole (HOBT)/N,N'-dicyclohexylcarbodiimide (DCC) in solution phase. Its antifungal activities and effects on strain growth were tested using the micro-broth dilution method and growth curves, respectively. Induced drug resistance in the C. albicans collection strain SC5314 was obtained by incubation with fluconazole (12 microg/mL) for 21 passages. Meanwhile, incubations with SL-A92 plus fluconazole were also carried out in SC5314 strains, and the MIC(80)s were used to evaluate the inhibitory effects of SL-A92 on drug resistance during the induction process. Real time RT-PCR was performed to investigate the CDR1 and CDR2 mRNA levels in induced SC5314 strains.

RESULTS

SC5314 strain induced by the combination of fluconazole and SL-A92 (200 microg/mL) did not develop drug resistance. On day 24, the CDR1 and CDR2 mRNA levels in SC5314 strain co-treated with fluconazole and SL-A92 relative to fluconazole alone were 26% and 24%, respectively, and on day 30 the CDR1 and CDR2 mRNA levels were 43% and 31%, respectively.

CONCLUSION

SL-A92 can block the development of drug resistance during the fluconazole induction process, which partially results from the down-regulation of CDR1 and CDR2.

A novel antifungal analog peptide derived from protaetiamycine

Previously, the 9-mer analog peptides, 9Pbw2 and 9Pbw4, were designed based on a defensin-like peptide, protaetiamycine isolated from Protaetia brevitarsis. In this study, antifungal effects of the analog peptides were investigated. The antifungal susceptibility testing exhibited that 9Pbw4 contained more potent antifungal activities than 9Pbw2. A PI influx assay confirmed the effects of the analog peptides and demonstrated that the peptides exerted their activity by a membrane-active mechanism, in an energy-independent manner. As the noteworthy potency of 9Pbw4, the mechanism(s) of 9Pbw4 were further investigated. The membrane studies, using rhodamine-labeled giant unilamellar vesicle (GUV) and fluorescein isothiocyanate (FITC)-dextran loaded liposome, suggested that the membrane-active mechanism of 9Pbw4 could have originated from the poreforming action and the radii of pores was presumed to be anywhere from 1.8 nm to 3.3 nm. These results were confirmed by 3D-flow cytometric contour-plot analysis. The present study suggests a potential of 9Pbw4 as a novel antifungal peptide.

The characteristics of Aspergillus fumigatus mycetoma development: is this a biofilm?

Aspergillus fumigatus is an increasingly prevalent opportunistic fungal pathogen of various immuno-compromised individuals. It has the ability to filament within the lungs forming dense intertwined mycelial balls. These morphological characteristics resemble those of microbial biofilms, which are matrix enclosed microbial populations, adherent to each other and/or to surfaces or interfaces. The purpose of this paper is to review some recent experiments that indicate the potential biofilm forming capacity of A. fumigatus in vitro. Initially it was established that conidial seeding density is important for stable biofilm development. In the optimized model conidial germination and filamentous growth characteristics were not observed until 8 h, after which a multi-cellular population expanded exponentially forming a thick structure (approx. 250 microm). Calcofluor white staining of this revealed the presence of extracellular polymeric matrix material, which increased as the biofilm matured. Subsequent antifungal sensitivity testing of this structure showed that azoles, polyenes and echinocandins were ineffective in reducing the cellular viability at therapeutically attainable concentrations. Microarray and real-time PCR analysis demonstrated the up-regulation of AfuMDR4 during multicellular growth and development, which may account the recalcitrance observed. Overall, A. fumigatus appears to possess the classical elements of biofilm growth, namely multicellularity, matrix production and sessile resistance. This controversial approach to understanding the biology of A. fumigatus infection may provide crucial information on how to treat this pathogenic fungus more effectively.

Development of a simple model for studying the effects of antifungal agents on multicellular communities of Aspergillus fumigatus

Aspergillus fumigatus is an increasingly prevalent opportunistic fungal pathogen of various immunocompromised individuals. It has the ability to form filaments within the lungs, producing dense intertwined mycelial balls, which are difficult to treat. The aim of this study was to develop a suitable model of A. fumigatus to examine the effects of antifungal challenge on these intertwined filamentous communities. A. fumigatus NCPF 7367 growth conditions were optimized on both Thermanox coverslips and on flat-bottomed microtitre plates to establish optimal conidial seeding densities. Isolates were treated with itraconazole, voriconazole, amphotericin B and caspofungin and their overall killing efficiency was measured using an XTT formazan metabolic dye assay. This was compared with the CLSI (formerly NCCLS) methodology of broth microdilution of moulds (standard M38-A). It was shown that 1x10(5) conidia ml(-1) in RPMI 1640 was the optimum concentration of spores for biofilm formation. Filamentous growth characteristics were not observed until 10 h incubation, followed by an exponential increase in the biofilm biomass (hyphae and extracellular material) and cellular activity (metabolism). When susceptibility testing of biofilms was compared with that of planktonic cells by CLSI broth microdilution testing, all antifungal drugs were at least 1000 times less effective at reducing the overall metabolic activity of 90 % of the cells. Overall, this study showed that A. fumigatus has the ability to form coherent multicellular biofilm structures that are resistant to the effects of antifungal drugs.

Comparison of two highly discriminatory molecular fingerprinting assays for analysis of multiple Aspergillus fumigatus isolates from patients with invasive aspergillosis

Two highly discriminatory fingerprinting assays, short tandem repeat typing and amplified fragment length polymorphism (AFLP), were compared to determine the genetic relatedness between 55 isolates of Aspergillus fumigatus obtained from 15 different patients suffering from proven invasive aspergillosis. Both techniques showed that interpatient isolates belonged to different genotypes and that intrapatient isolates from deep sites were all of the same genotype. By contrast, multiple genotypes were found among isolates originating from respiratory samples. Both techniques have specific advantages and disadvantages. AFLP is more universally applicable, but short tandem repeat analysis offers better discriminatory power and should be the preferred method for standardizing typing of clinical isolates of Aspergillus fumigatus.

Fcr1p inhibits development of fluconazole resistance in Candida albicans by abolishing CDR1 induction

Overexpression of Candida drug resistance 1 (CDR1) gene in Candida albicans (C. albicans), an efflux pump, is one of the major mechanisms contributing to drug resistance. C. albicans for fluconazole resistance 1 protein (Fcr1p) is a member of the family of zinc cluster proteins homologous to Pdr1p and Pdr3p (pleiotropic drug resistance protein) mediating azole resistance in Saccharomyces cerevisiae (S. cerevisiae) by regulating the expression of pleiotropic drug resistance 5 (PDR5) homologous to C. albicans CDR1. A previous study has showed that for fluconazole resistance 1 (FCR1) could also confer azole resistance in S. cerevisiae pdr1 pdr3 mutant by regulating PDR5. Therefore, we investigated the role of FCR1 in the development of C. albicans azole resistance in vitro and in vivo. Our results showed that Fcr1p inhibited fluconazole (FLC) resistance development in C. albicans through abolishing the induction of CDR1 expression by FLC, and in contrast FLC resistance development was accelerated resulting from the deletion of FCR1.

Cap1p is involved in multiple pathways of oxidative stress response in Candida albicans

Cap1p, a transcription factor in Candida albicans, is thought to participate in oxidative stress tolerance, but the pathways involved are still unclear. The study was designed to reveal the possible pathways by examining changes in the transcription profile after H2O2 treatment with both the cap1-deleted strain CJD21 and its parental strain CAI4 using microarray analysis. Of the identified 89 genes differentially expressed in CAI4 after exposure to H2O2, 76 genes were in a Cap1p-dependent expression pattern. We have shown that Cap1p is involved in the oxidative stress response in C. albicans via multiple pathways, including the cellular antioxidant defense system (e.g., thioredoxin reductase, glutathione reductase, glutathione S-transferase), carbohydrate metabolism and energy metabolism (e.g., glucose-6-phosphate dehydrogenase, transaldolase, glyoxalase I, NADH-dependent flavin oxidoreductase), protein degradation (e.g., 26S proteasome regulatory subunit, ubiquitin-specific protease), ATP-dependent RNA helicase (e.g., DEAD box protein ATP-dependent RNA helicase), and resistance pathways (e.g., multidrug resistance protein, ABC transporter essential for cadmium resistance). Real-time reverse transcription-PCR analysis further confirmed the results of microarray. Collectively, this study provides new insight into the biological functions of Cap1p in oxidative stress response.

Predictive value of oral colonization by Candida yeasts for the onset of a nosocomial infection in elderly hospitalized patients

The incidence of nosocomial yeast infections has increased markedly in recent decades, especially among the elderly. The present study was therefore initiated not only to determine the predictive value of oral colonization by yeasts for the onset of a nosocomial Candida infection in elderly hospitalized patients (>65 years), but also to clarify the factors that promote infection and to establish a relationship between the intensity of oral carriage and the onset of yeast infection. During this prospective cohort study, 256 patients (156 women and 100 men with a mean age of 83±8 years) were surveyed for yeast colonization or infection. Samples were collected every 4 days from day 0 to day 16 from four sites in the mouth, and intrinsic and extrinsic factors that might promote infection were recorded for each patient. Pulsed field gel electrophoresis was performed on Candida albicans isolates from all infected patients. Poor nutritional status was observed in 81 % of the patients and hyposalivation in 41 %. The colonization level was 67 % on day 0 (59 % C. albicans) and a heavy carriage of yeasts (>50 c.f.u.) was observed for 51 % of the patients. The incidence of nosocomial colonization reached 6·9 % on day 4 (6·1 % on day 8 and 2·7 % on day 12), and that of nosocomial infection was 3·7 % on day 4 (6·8 % on day 8, 11·3 % on day 12 and 19·2 % on day 16). Of the 35 patients infected, 57 % were suffering from oral candidiasis. The principal risk factors for colonization were a dental prosthesis, poor oral hygiene and the use of antibiotics. The risk factors for infection, in addition to those already mentioned for colonization, were endocrine disease, poor nutritional status, prolonged hospitalization and high colony counts. Genotyping revealed person-to-person transmission in two patients. Thus, this study demonstrates a significant association between oral colonization and the onset of yeast infections in elderly hospitalized patients. Therefore, oral samples should be collected at admission and antifungal treatment should be administered in cases of colonization, especially in patients presenting a heavy carriage of yeasts. Genotyping of the strains confirmed the possibility of person-to-person transmission.

Excess mortality, length of stay, and costs associated with serious fungal infections among elderly cancer patients: findings from linked SEER-Medicare data

OBJECTIVE

To calculate the excess mortality, length of stay, and costs attributable to serious fungal infections in hospitalized elderly patients with selected cancers.

METHODS

This study involved a retrospective cohort analysis using linked data from the Surveillance, Epidemiology and End Results Program of the National Cancer Institute (SEER) and Medicare claims data. Study cohorts included patients aged 65 years and older who newly received a diagnosis of a selected cancer (acute myeloid leukemia [AML] or squamous cell carcinoma of the head and neck [SCCHN]) in a SEER registry between 1991 and 1996 and who had a subsequent diagnosis of a serious fungal infection during an inpatient hospitalization, and hospitalized controls without a fungal infection matched 1:1 by age, geographic region, receipt of recent chemotherapy, concomitant bacterial infection, timing of the index hospitalization, and cancer stage at diagnosis (for SCCHN patients only).

RESULTS

Eighty AML patients and 52 SCCHN patients experienced a serious fungal infection involving hospitalization. Relative to matched controls, SCCHN patients with fungal infections had significantly higher all-cause mortality (40% vs. 14%, P = 0.002), while mortality rates did not differ between AML cohorts. Patients with fungal infections had significantly longer index hospitalizations regardless of cancer type (mean: 30 days vs. 19 days for AML patients; 20 days vs. 9 days for SCCHN patients), and correspondingly higher Medicare payments (mean +/- SD: 34,268 dollars +/- 31,811 dollars vs. 21,416 dollars +/- 22,449 dollars among AML patients, P < 0.0001; 25,942 dollars +/- 29,122 dollars vs. 10,131 dollars +/- 10,686 dollars among SCCHN patients, P < 0.0001).

CONCLUSIONS

Efforts to prevent these infections and/or initiate early treatment may yield both clinical and economic benefits.

A new group of antifungal and antibacterial lipopeptides derived from non-membrane active peptides conjugated to palmitic acid

We report on the synthesis, biological function, and a plausible mode of action of a new group of lipopeptides with potent antifungal and antibacterial activities. These lipopeptides are derived from positively charged peptides containing d- and l-amino acids (diastereomers) that are palmitoylated (PA) at their N terminus. The peptides investigated have the sequence K(4)X(7)W, where X designates Gly, Ala, Val, or Leu (designated d-X peptides). The data revealed that PA-d-G and PA-d-A gained potent antibacterial and antifungal activity despite the fact that both parental peptides were completely devoid of any activity toward microorganisms and model phospholipid membranes. In contrast, PA-d-L lost the potent antibacterial activity of the parental peptide but gained and preserved partial antifungal activity. Interestingly, both d-V and its palmitoylated analog were inactive toward bacteria, and only the palmitoylated peptide was highly potent toward yeast. Both PA-d-L and PA-d-V lipopeptides were also endowed with hemolytic activity. Mode of action studies were performed by using tryptophan fluorescence and attenuated total reflectance Fourier transform infrared and circular dichroism spectroscopy as well as transmembrane depolarization assays with bacteria and fungi. The data suggest that the lipopeptides act by increasing the permeability of the cell membrane and that differences in their potency and target specificity are the result of differences in their oligomeric state and ability to dissociate and insert into the cytoplasmic membrane. These results provide insight regarding a new approach of modulating hydrophobicity and the self-assembly of non-membrane interacting peptides in order to endow them with both antibacterial and antifungal activities urgently needed to combat bacterial and fungal infections.

Evaluation of a polymerase chain reaction reverse hybridization line probe assay for the detection and identification of medically important fungi in bronchoalveolar lavage fluids

An assay system in which polymerase chain reaction (PCR) amplification of the ITS-1 region of ribosomal DNA (rDNA) is combined with a reverse-hybridization line probe assay (LiPA) was used for the identification of six Candida species and four Aspergillus species in pure cultures of clinical isolates, as well as in bronchoalveolar lavage (BAL) fluid samples from 42 patients with various underlying diseases. The results were compared with the results obtained with conventional routine identification methods as well as with a commercial enzyme-linked immunosorbent assay (ELISA) galactomannan detection assay and an Aspergillus-specific PCR. No discrepancies between the PCR-LiPA system and routine methods were found for pure cultures of Candida and Aspergillus species except in the case of Aspergillus versicolor. In BAL fluid samples in which Candida species were cultured, the PCR-LiPA system identified more species than did the routine methods. When routine analyses of patient samples were supplemented by adding data obtained by repurifying and re-identifying cultures and by taking isolates obtained from other body sites into account, the results agreed with PCR-LiPA system results in 81% of the cases (34/42). Most of the remaining discrepancies (6/8) involved cases in which such supplementary data were not available. In BAL fluid samples from which A. fumigatus was cultured, the agreement between the PCR-LiPA system and the routine methods was low. Only 2 of 11 BAL samples shown to contain A. fumigatus in ELISA and genus-specific PCR assays were positive in PCR-LiPA system. The PCR-LiPA system enables the simultaneous detection and identification of different fungal species present in pure or mixed populations within 6 h in a single assay. Optimization is required, however, before it is useful as a diagnostic tool in the clinical microbiology laboratory.