Development of a method to detect and quantify <Emphasis Type="Italic">Aspergillus fumigatus</Emphasis> conidia by quantitative PCR for environmental air samples

Exposure to Aspergillus fumigatus is linked with respiratory diseases such as asthma, invasive aspergillosis, hypersensitivity pneumonitis, and allergic bronchopulmonary aspergillosis. Molecular methods using quantitative PCR (qPCR) offer advantages over culture and optical methods for estimating human exposures to microbiological agents such as fungi. We describe an assay that uses lyticase to digest A. fumigatus conidia followed by TaqMan™ qPCR to quantify released DNA. This method will allow analysis of airborne A. fumigatus samples collected over extended time periods and provide a more representative assessment of chronic exposure. The method was optimized for environmental samples and incorporates: single tube sample preparation to reduce sample loss, maintain simplicity, and avoid contamination; hot start amplification to reduce non-specific primer/probe annealing; and uracil-N-glycosylase to prevent carryover contamination. An A. fumigatus internal standard was developed and used to detect PCR inhibitors potentially found in air samples. The assay detected fewer than 10 A. fumigatus conidia per qPCR reaction and quantified conidia over a 4−log₁₀ range with high linearity (R ² > 0.99) and low variability among replicate standards (CV=2.0%) in less than 4 h. The sensitivity and linearity of qPCR for conidia deposited on filters was equivalent to conidia calibration standards. A. fumigatus DNA from 8 isolates was consistently quantified using this method, while non-specific DNA from 14 common environmental fungi, including 6 other Aspergillus species, was not detected. This method provides a means of analyzing long term air samples collected on filters which may enable investigators to correlate airborne environmental A. fumigatus conidia concentrations with adverse health effects.     

Susceptibility of Larvae of Galleria mellonella to Infection by Aspergillus fumigatus is Dependent upon Stage of Conidial Germination

The ability of conidia of the human pathogenic fungus Aspergillus fumigatus to kill larvae of the insect Galleria mellonella was investigated. Conidia at different stages of the germination process displayed variations in their virulence as measured using the Galleria infection model. Non-germinating (‘resting’) conidia were avirulent except when an inoculation density of 1 × 10⁷ conidia per insect was used. Conidia that had been induced to commence the germination process by pre-culturing in growth medium for 3 h were capable of killing larvae at densities of 1 × 10⁶ and 1 × 10⁷ per insect. An inoculation density of 1 × 10⁵ conidia per insect remained avirulent. Conidia in the outgrowth phase of germination (characterised as the formation of a germ tube) were the most virulent and were capable of killing 100% of larvae after 5 or 24 h when 1 × 10⁷ or 1 × 10⁶ conidia, that had been allowed to germinate for 24 h, were used. Examination of the response of insect haemocytes to conidia at different stages of the germination process established that haemocytes could engulf non-germinating conidia and those in the early stages of the germination process but that conidia, which had reached the outgrowth stages of germination were not phagocytosed. The results presented here indicate that haemocytes of G. mellonella are capable of phagocytosing A. fumigatus conidia less than 3.0 μm in diameter but that conidia greater than this are too large to be engulfed. The virulence of A. fumigatus in G. mellonella larvae can be ascertained within 60–90 h if infection densities of 1 × 10⁶ or 1 × 10⁷ activated conidia (pre-incubated for 2–3 h) per insect are employed.     

Effects of extracts of fiberglass insulations on the growth ofAspergillus fumigatus andA. versicolor

Water extracts of thermal and acoustic fiberglass insulations used in the duct work of heating, ventilation and air conditioning (HVAC) systems supported germination of conidia and growth ofAspergillus versicolor (Vuillemin) Tiraboschi 1908–9 andAspergillus fumigatus Fresenius 1863. Urea, formaldehyde and unidentified organics were detected in the extracts. Formaldehyde in concentrations similar to those found in the extracts restricted the growth of both species in enriched media.A. versicolor, the more common species associated with fiberglass insulations, was more resistant to formaldehyde thanA. fumigatus.     

Comparative study of Aspergillus mycotoxin production on enriched media and construction material

Isolates of Aspergillus flavus and Aspergillus fumigatus from indoor air were compared with a known mycotoxin producer for their capacity to produce mycotoxins on a variety of enrichment media and with growth on indoor substrates such as ceiling tile and wall board. In enrichment media, four of seven isolates of A. flavus produced at least one aflatoxin and both isolates of A. fumigatus produced mycotoxins. The spectrum of mycotoxins and their concentrations varied with the strain and medium. When the mycotoxin-positive strains were grown to a dense concentration on indoor construction and finishing materials such as ceiling tile and wall boards, mycotoxins were not detected in extracts of the materials. Colonization of indoor surfaces by mycotoxin-producing strains of A. flavus and A. fumigatus may not necessarily expose inhabitants to mycotoxins or result in production of mycotoxins. Received 09 February 1999/ Accepted in revised form 28 June 1999     

Pathogenicity, formulation and storage of insect pathogenic hyphomycetous fungi tested against Diabrotica speciosa

Studies were conducted tosearch for fungal strains with potentialpathogenicity against Diabrotica speciosa(Germar) (Coleoptera: Chrysomelidae).Among sixteen fungal isolates screenedthe most virulent was a Beauveria bassiana(Balsamo) Vuillemin isolate (FHD13) thatcaused 70% mortality of D. speciosathird instar larvae. The LC₅₀ value ofB. bassiana isolate FHD13 was3.48 × 10¹⁰ conidia/ml.Different temperatures (4, 17 and 26 °C)and vegetable oils (corn, sunflower and canola)used for storage did not significantly affectviability of conidia. A pathogenicity trialagainst D. speciosa larvae performed withthe corn oil formulation (1 × 10⁸ conidia/mlof oil) caused 65% of mortality.     

Toxinogenèse in vitro d'Aspergillus du groupe fumigatus. Production de fumitoxines

A new class of mycotoxins has been characterized from a strain of Aspergillus fumigatus: the fumitoxins A, B, C and D. The in vitro production of these metabolites is studied. Fumitoxins are common in cultures extracts of most strains of A. fumigatus. They are not detected from A. fischeri. Variations of the levels of these products during the incubation of cultures, and also by using different media, are noted. At all events, the toxicity of crude extracts of the mould, for the chick embryo, is equal to the one of the fumitoxins.

     

Effects of Conidia of Various Aspergillus Species on Apoptosis of Human Pneumocytes and Bronchial Epithelial Cells

Aspergillus species can cause mycoses in human and animals. Previously, we demonstrated that A. fumigatus conidia from a human isolate inhibited apoptosis in human pneumocytes and bronchial epithelial cells. In the current study, we studied the effects of A. fumigatus conidia non-human origin and A. flavus, A. nidulans, A. niger and A. oryzae conidia on human cells apoptosis. Human pneumocytes or bronchial epithelial cells were simultaneously exposed to apoptotic inductors and aspergilli conidia. The cell cultures were analyzed by flow cytometry, immunoblotting, and examination of nuclear morphology. Similar to A. fumigatus conidia, A. flavus conidia inhibited cellular apoptosis while A. nidulans, A. niger and A. oryzae conidia did not affect apoptosis. We further studied the species specificity of conidia: there were no differences in the inhibition of apoptosis by A. fumigatus conidia from either human or bird isolates. In order to determine whether the inhibition of apoptosis by conidia is limited to certain strains, the effect on human cell apoptosis of different A. fumigatus human clinical isolates and A. fumigatus of environmental origin was evaluated. All A. fumigatus isolates inhibited apoptosis; an anti-apoptotic factor was released by conidia. For TNF-induced apoptosis, the anti-apoptotic effect of conidia of all isolates was found to be associated with a reduction of caspase-3 in human cells. The results suggest that suppression of apoptosis may play a role in reducing the efficacy of host defense mechanisms during infection with Aspergillus species. F. Féménia and D. Huet made an equal contribution to this work.     

Discrepancies between MIC and MLC values of amphotericin B against isolates ofAspergillus species

There is little information addressing the phenomena of discrepancy between minimal inhibitory concentrations (MIC) and minimal lethal concentrations (MLC) values of amphotericin B (AMB) to clinical isolates of fungi. This study assessed in vitro activity of AMB against 70 clinical isolates of aspergilli: 30 strains ofAspergillus fumigatus, 20 strains ofAspergillus flavus and 20 strains ofAspergillus niger. Susceptibility tests were accomplished using a macro broth dilution procedure, with special emphasis on ascertainment of MLCs. AMB exhibited low MIC values against all clinical isolates. While we did not identify any AMB resistant isolates among 70Aspergillus spp. studied as judged by MIC levels, analysis of the data demonstrated a clear discrepancy between the MIC and MLC levels of AMB obtained against clinical isolates ofAspergillus spp. The MLC values of AMB were significantly higher than the MIC values with MIC 50 and MIC 90 of 0.29 and 0.5 µg/ml, respectively, at the second reading time, and MLC 50 and MLC 90 of 2.31 and 9.24 µg/ml, respectively (p<0.001). Additionally, minimal lethal concentrations in 36/70 (51%) of aspergillal isolates studied produced drug concentrations above those which can usually be sustained in patient plasma or tissue.     

MonitoringAspergillus fumigatus aerosols from a composting facility

The large, outdoor Islip Yard Waste Composting Facility on Long Island, New York was investigated as a source of airborne fungus spores. The Burkard-Hirst volumetric spore trap was used for the first extensive sampling of small mold spores for this application. Samplers were operated continuously from 21 August to 30 November 1992 in the facility and in a suburban community about 540 m from the facility. A control site approximately 10 000 m from the facility was also sampled to establish background levels of fungus spores. The facility site had higher average readings ofAspergillus fumigatus spores than did the community and both were higher than the control.A. fumigatus was the only fungus among 30 categories tracked that differed significantly between the facility and control sites. It was also isolated repeatedly from the compost. Higher average levels ofA. fumigatus were measured in the community when winds blew from the facility, and also during times when the compost was moved or mixed at the facility. No correlation was found between wind direction or work times andA. fumigatus conidia at the control site. The study shows that this compost facility can produce a measurable increase in the number of airborneA. fumigatus conidia both at the edge of the facility and at 540 m downwind. It also demonstrates that the Burkard spore trap can be used for monitoring small, airborne mold spores, but it is a difficult and labor intensive task.     

Aspergillus fumigatus adhesion factors in dormant conidia revealed through comparative phenotypic and transcriptomic analyses

Aspergillus fumigatus is an important fungal pathogen of humans. Inhaled conidia of A. fumigatus adhere to pulmonary epithelial cells, causing opportunistic infection. However, little is known about the molecular mechanism of the adherence of resting conidia. Fungal molecules adhesive to host cells are presumed to be displayed on the conidial surface during conidial formation as a result of changes in gene expression. Therefore, we exhaustively searched for adhesion molecules by comparing the phenotypes and the gene expression profiles of A. fumigatus strains that have conidia showing either high or low adherence to human pulmonary A549 cells. Morphological observation suggested that strains that produce conidia of reduced size, hydrophobicity, or number show decreased adherence to A549 cells. K‐means cluster analyses of gene expression revealed 31 genes that were differentially expressed in the high‐adherence strains during conidial formation. We knocked out three of these genes and showed that the conidia of AFUA_4G01030 (encoding a hypothetical protein) and AFUA_4G08805 (encoding a haemolysin‐like protein) knockout strains had significantly reduced adherence to host cells. Furthermore, the conidia of these knockout strains had lower hydrophobicity and fewer surface spikes compared to the control strain. We suggest that the selectively expressed gene products, including those we identified experimentally, have composite synergistic roles in the adhesion of conidia to pulmonary epithelial cells.     

金龟子绿僵菌在森林土壤中的分布及对松墨天牛致病性测定

松墨天牛是重大森林植物检疫性病害——松材线虫病的主要媒介昆虫。本研究于2005年8月～2006年8月从福建、江西两省共110个林分样区（其中松林88个样区）采集土壤样品330份,采用选择性培养基分离土壤中的金龟子绿僵菌。从21个样区的26份土样中分离出的金龟子绿僵菌占采集样区的19.1%和样品的7.9%,成菌落数（CFU）500～72500CFU/g,表明金龟子绿僵菌在森林土壤中有较为广泛的分布。对分离到的9个产孢量高的菌株,采用浸渍法（1×10⁷孢子/mL）接种3～4龄健康松墨天牛幼虫,采用跗节接种法接种2～15日龄健康成虫,测定其致病力。结果表明,MaYTTR-03、MaYTTR-04菌株对松墨天牛幼虫和成虫均有较高致病力,表现出良好的生防潜力。     

In vitro determination of phagocytosis and intracellular killing of Aspergillus species by mononuclear phagocytes

We investigated phagocytosis and intracellular killing of clinical and environmental isolates of Aspergillus spp. by human monocyte-derived macrophages (MDMs). Serial pathogens such as Aspergillus fumigatus, Aspergillus flavus and Aspergillus terreus were examined with a microbiological assay. Phagocytosis for resting conidia of Aspergillus spp. was similar for all isolates tested. During 30 min of incubation phagocytosis ranged from 49.9% to 85.5% for clinical isolates and from 40.3% to 87.1% for environmental isolates. MDMs killed A. fumigatus, A. flavus and A. terreus conidia after ingestion for 120 min, as shown by a decrease in colony forming units (cfu) count of intracellular fungi. The killing index for all isolates of Aspergillus spp., ranged from 12.1 ± 1.1% to 90.3 ± 10.4%; isolate-dependent (P < 0.01) differences against the fungicidal action of MDMs were observed. In conclusion, significant differences were noted for killing indices between several strains of Aspergillus spp. whereas phagocytosis was similar for all isolates tested in vitro. No differences were observed within environmental and clinical isolates.     

Effect of Peroxynitrite on dormant spores and germlings ofAspergillus fumigatus in vitro

Peroxynitrite was tested for its effects on the opportunistic pathogenic fungusAspergillus fumigatus. It did not kill any dormant or swollen (4 h in a glucose-peptone medium) conidia in concentrations up to 6.25 mmol/L and the growth of germlings (after 6 or 9 h) was only slightly inhibited by 5 mmol/L peroxynitrite. The peroxynitrite donor SIN-1 (up to 10 mmol/L, I d in buffer) did not kill any conidia but inhibited their germination and growth, depending on the medium. Ten mmol/L SIN-1 in a poor medium was fungistatic and germination was stopped for 20 h. Nine strains ofA. fumigatus showed resistance comparable to the model strain, while 6Candida albicans strains were much more susceptible to both peroxynitrite and its donor. The results indicate that peroxynitrite does not contribute substantially to the antifungal activity of phagocytes againstA. fumigatus.     

The significance of Cognettia sphagnetorum(Enchytraeidae) on nitrogen availability and plant growth in wood ash-treated humus soil

A laboratory microcosm experiment was established to study whether the role of Cognettia sphagnetorum (Enchytraeidae) in affecting Scots pine (Pinus sylvestris) seedling growth is influenced by wood ash-amendment, i.e., neutralisation of the raw humus soil. Coniferous forest soil, inoculated with soil microbes and nematodes, was either treated with wood ash or left as ash-free control. Wood ash (corresponding to an amount of 5000 kg ha^–1) was either spread on the soil surface or mixed into the soil. Enchytraeid and pine seedling biomass, abundance of nematodes, and water leachable NH₄ ⁺-N and NO₃ ^–-N were measured 26 and 51 weeks after initiation of the experiment and root length and N concentration of needles were measured 51 weeks after initiation of the experiment. Wood ash when mixed into the soil, reduced the biomass of C. sphagnetorum. Nematodes were unaffected by the treatments. In the ash-free soils C. sphagnetorum had little influence on pine growth, but it did decrease root length and root to shoot ratio. In the absence of enchytraeids wood ash decreased pine biomass production and root length. However, the presence of enchytraeids in the ash-treated soil compensated the ash-induced negative effects on the pine performance. Enchytraeids increased and wood ash decreased water leachable NH₄ ⁺-N in the presence but not in the absence of enchytraeids, while water leachable NO₃ ^–-N was not affected by the treatments. It was concluded that C. sphagnetorum can be important in ensuring nutrient cycling and plant growth in situations when an ecosystem encounters disturbances.     

Verruculogen associated with <Emphasis Type="Italic">Aspergillus fumigatus</Emphasis> hyphae and conidia modifies the electrophysiological properties of human nasal epithelial cells

Background  

The role of Aspergillus fumigatus mycotoxins in the colonization of the respiratory tract by conidia has not been studied extensively, even though patients at risk from invasive aspergillosis frequently exhibit respiratory epithelium damage. In a previous study, we found that filtrates of A. fumigatus cultures can specifically alter the electrophysiological properties of human nasal epithelial cells (HNEC) compared to those of non pathogenic moulds.     

Interaction of cotton tissue culture cells andVerticillium dahliae

Summary Elicitation of sesquiterpenoid aldehyde phytoalexins inGossypium arboreum cell suspension cultures was confirmed by thin layer chromatography, high performance reverse phase liquid chromatography, and an aniline-reaction assay after inoculation with heat-treated conidia ofVerticillium dahliae A 2.3X mean increase in total terpenoids was observed. Component phytoalexins varied, with either hemigossypol and gossypol being detected or the O-methylated terpenoids hemigossypol-6-methyl ether and related compounds. Long-termGossypium suspension cultures were mixoploid with an increase in chromosome number and mean DNA content. Addition ofV. dahliae elicitor(s) to the medium for embryo-proliferating callus ofG. hirsutum inhibited growth and embryo production with a linear correlation (r=−0.87;P<0.01) between the elicitor concentration and the number of embryos. Addition of¹⁴C-labeled NaOAc to suspension cells gave 30% incorporation, and from¹³C-NaOAc addition, labeled sesquiterpenoid aldehydes were recovered. The cotton-Verticillium system is another case of secondary metabolite elicitation in plant tissue culture and might be used for basic studies of hostpathogen interaction as well as for a selection tool to obtain resistance to an important disease.     

Fusarium fractiflexum sp. nov. and two other species within theGibberella fujikuroi species complex recently discovered in Japan that form aerial conidia in false heads

Morphological and molecular phylogenetic analyses were conducted on 12 strains ofFusarium, deposited in MAFF asF. subglutinans (≡F. moniliforme var.subglutinans≡F. sacchari var.subglutinans) orFusarium sp. because they formed aerial conidia in false heads in the dark. These strains were resolved as three distinct species within theGibberella fujikuroi species complex. A new species,F. fractiflexum, and two species new to Japan,F. circinatum andF. concentricum, are described and illustrated and their morphological features are discussed.Fusarium fractiflexum, isolated from diseased yellow leaf spots ofCymbidium spp., is differentiated from other fusaria based on its yellowish colonies and aerial conidia formed in false heads in the dark and in zigzag-like conidial chains under black light. Japanese strains ofF. circinatum also formed elongate, coiled sterile hyphae. Phialidic aerial conidia with a pointed apex and a wedgeshaped base were found inF. concentricum cultured under black light and represent a new diagnostic character of the species, in addition to colonies with alternating concentric rings when cultured on PDA. Based on DNA sequences of the β-tubulin gene and two other loci, strains ofF. fractiflexum were resolved phylogenetically as members of the Asian clade of theG. fujikuroi species complex. In addition, Japanese strains ofF. circinatum andF. concentricum were phylogenetically identical to the ex-type strains.     

Conidia of Trichoderma virens as a phosphorus source for mycorrhizal Pinus sylvestris seedlings

In this study, the mobilization and further translocation of phosphorus from conidia of saprotrophic fungus Trichoderma virens into Pinus sylvestris seedlings by nondestructive measuring of ³²P was assessed. The radioactive phosphorus flux from the conidia to the Scots pine seedlings forming mycorrhiza with Laccaria laccata and Suillus bovinus amounted up to 27.82% and 7.42%, respectively, on the 28th day of the experiment, while at the same time in nonmycorrhizal pine seedlings, the detected radioactivity reached only 0.56%. Our studies revealed that both ectomycorrhizal fungi: L. laccata and S. bovinus, mobilized the phosphorus from radioactive conidia of T. virens. On this basis, we conclude that activities of the mycosymbionts may facilitate absorption and further translocation of phosphorus from organic matter into the host plants.     

Abundant Respirable Ergot Alkaloids from the Common Airborne Fungus Aspergillus fumigatus

Ergot alkaloids are mycotoxins that interact with several monoamine receptors, negatively affecting cardiovascular, nervous, reproductive, and immune systems of exposed humans and animals. Aspergillus fumigatus, a common airborne fungus and opportunistic human pathogen, can produce ergot alkaloids in broth culture. The objectives of this study were to determine if A. fumigatus accumulates ergot alkaloids in a respirable form in or on its conidia, to quantify ergot alkaloids associated with conidia produced on several different substrates, and to measure relevant physical properties of the conidia. We found at least four ergot alkaloids, fumigaclavine C, festuclavine, fumigaclavine A, and fumigaclavine B (in order of abundance), associated with conidia of A. fumigatus. Under environmentally relevant conditions, the total mass of ergot alkaloids often constituted >1% of the mass of the conidium. Ergot alkaloids were extracted from conidia produced on all media tested, and the greatest quantities were observed when the fungus was cultured on latex paint or cultured maize seedlings. The values for physical properties of conidia likely to affect their respirability (i.e., diameter, mass, and specific gravity) were significantly lower for A. fumigatus than for Aspergillus nidulans, Aspergillus niger, and Stachybotrys chartarum. The demonstration of relatively high concentrations of ergot alkaloids associated with conidia of A. fumigatus presents opportunities for investigations of potential contributions of the toxins to adverse health effects associated with the fungus and to aspects of the biology of the fungus that contribute to its success.