Hydrocortisone, prednisolone and dexamethasone act on Aspergillus fumigatus in vitro susceptibility to itraconazole

In a previous in vitro investigation from the same laboratory a therapeutic level of hydrocortisone enhanced the itraconazole susceptibility of a single strain of Aspergillus fumigatus. In the present work, the influence of therapeutic levels of hydrocortisone (1 microM), prednisolone (0.125 microM 0.25 microM and 0.5 microM) and dexamethasone (0.25 microM and 0.5 microM) on the itraconazole susceptibility of four A. fumigatus strains, was determined. A. fumigatus conidia were germinated either in the absence or in the presence of a glucocorticoid. The germinated conidia were then spread onto plates and grown either in the presence or in the absence of a glucocorticoid, together with increasing concentrations of itraconazole. The mean colony forming units (CFU) were measured. Two factor analyses of variance showed that hydrocortisone significantly (p <0.001) potentiated the action of itraconazole. The cytotoxic effect of prednisolone on the fungal strains added significantly to the effect of itraconazole (p <0.001). Dexamethasone was also cytotoxic to the fungus but, when used in conjunction with itraconazole, it effectively increased (p <0.01) the number of CFU. This study showed a direct effect of glucocorticoids, currently in use for patient therapy, on in vitro A. fumigatus susceptibility to itraconazole.     

Mechanisms of antifungal resistance

The many drugs that are available at present to treat fungal infections can be divided into four broad groups on the basis of their mechanism of action. These antifungal agents either inhibit macromolecule synthesis (flucytosine), impair membrane barrier function (polyenes), inhibit ergosterol synthesis (allylamines, thiocarbamates, azole derivatives, morpholines), or interact with microtubules (griseofulvin). Drug resistance has been identified as the major cause of treatment failure among patients treated with flucytosine. A lesion in the UMP-pyrophosphorylase is the most frequent clinical determinant of resistance to 5FC in Candida albicans. Despite extensive use of polyene antibiotics for more than 30 years, emergence of acquired resistance seems not be a significant clinical problem. Polyene-resistant Candida isolates have a marked decrease in their ergosterol content. Acquired resistance to allylamines has not been reported from human pathogens, but, resistant phenotypes have been reported for variants of Saccharomyces cerevisiae and of Ustilago maydis. Tolerance to morpholines is seldom found. Intrinsic resistance to griseofulvin is due to the absence of a prolonged energy-dependent transport system for this antibiotic. Resistance to azole antifungal agents is known to be exceptional, although it does now appear to be increasing in importance in some groups of patients infected with e.g. Candida spp., Histoplasma capsulatum or Cryptococcus neoformans. For example, resistance to fluconazole is emerging in C. albicans, the major agent of oro-pharyngeal candidosis in AIDS patients, after long-term suppressive therapy. In the majority of cases, primary and secondary resistance to fluconazole and cross-resistance to other azole antifungal agents seems to originate from decreased intracellular accumulation of the azoles, which may result from reduced uptake or increased efflux of the molecules. In most C. albicans isolates the decreased intracellular levels can be correlated with enhanced azole efflux, a phenomenon linked to an increase in the amounts of mRNA of a C. albicans ABC transporter gene CDR1 and of a gene (BEN(r) or CaMDR) coding for a transporter belonging to the class of major facilitator multidrug efflux transporters. Not only fluconazole, ketoconazole and itraconazole are substrates for CDR1, terbinafine and amorolfine have also been established as substrates, BEN(r) overexpression only accounts for fluconazole resistance. Other sources of resistance: changes in membrane sterols and phospholipids, altered or overproduced target enzyme(s) and compensatory mutations in the Delta5,6-desaturase.     

Aspergillus fumigatus catalases: cloning of an Aspergillus nidulans catalase B homologue and evidence for at least three catalases

The presence of catalases in the water soluble fractions of three Aspergillus fumigatus strains was investigated using non-denaturing and denaturing polyacrylamide gel electrophoresis and Western analysis. Using non-denaturing polyacrylamide gel electrophoresis and staining for catalase activity, three separate catalases were identified. An A. fumigatus catalase gene (catB) was cloned from genomic DNA using the Aspergillus niger catR gene as a probe. Polyclonal antibodies were raised to a glutathione S-transferase-CatB fusion product expressed in Escherichia coli. Western analysis indicated that, under denaturing conditions, the polyclonal antibody recognised a 90-kDa band and under non-denaturing conditions, two separate bands were identified. These results indicate that A. fumigatus in addition to CatB, produces at least two other catalases, one of which is similar in size to CatB. The polyclonal antibody was also used to observe catalase expression in mice, experimentally infected with A. fumigatus. Staining was observed heterogeneously throughout the fungal hyphae. This result indicates that catalase is produced by A. fumigatus during invasive aspergillosis.     

额外拷贝ERG6基因对烟曲霉的影响

通过构建烟曲霉ERG6基因额外拷贝株．研究该基因对烟曲霉生长速度、抗药物敏感性的影响。在烟曲霉基因组找出烟曲霉可能的ERG6基因的开放读码框(ORF),PCR扩增ERG6的ORF连同其上下游各约1 kb的DNA片段,利用DNA重组的方法将该片段克隆到载体pRG-AMA1-NotI。用重组后的质粒转化烟曲霉尿嘧啶营养缺陷株AF293．1。在MM和YAG培养基上观察转化子的生长速度。采用纸片扩散法和微量液基稀释法测定转化子对抗真菌药物敏感性。烟曲霉基因组中存在一个拷贝的ERG6基因,ORF大小为1,256 bp。其编码的蛋白与白念珠菌、酿酒酵母固醇甲基转移酶(Ers6p)的氨基酸相同率分别为57%和50%,相似率分别为70%和63%。烟曲霉中ERG6基因被成功克隆到了pRG-AMA1-Not I,产生了质粒pERG6。用pERG6和空载体pRG-AMA1-Not I转化AF293．1后,分别得到转化子AF-pERG6和AF-empty。AF-pERG6在MM和YAG培养基上的生长速度均比AF-empty慢。AF-pERG6和AF-empty对伊曲康唑、伏力康唑、特比萘芬、两性霉素B、卡泊芬净、灰黄霉素的敏感性没有差异。ERG6基因额外拷贝不影响烟曲霉对伊曲康唑、伏力康唑、特比萘芬、两性霉素B、卡泊芬净、灰黄霉素的敏感性,但是能使烟曲霉的生长速度减慢。     

Essential gene identification and drug target prioritization in Aspergillus fumigatus

Aspergillus fumigatus is the most prevalent airborne filamentous fungal pathogen in humans, causing severe and often fatal invasive infections in immunocompromised patients. Currently available antifungal drugs to treat invasive aspergillosis have limited modes of action, and few are safe and effective. To identify and prioritize antifungal drug targets, we have developed a conditional promoter replacement (CPR) strategy using the nitrogen-regulated A. fumigatus NiiA promoter (pNiiA). The gene essentiality for 35 A. fumigatus genes was directly demonstrated by this pNiiA-CPR strategy from a set of 54 genes representing broad biological functions whose orthologs are confirmed to be essential for growth in Candida albicans and Saccharomyces cerevisiae. Extending this approach, we show that the ERG11 gene family (ERG11A and ERG11B) is essential in A. fumigatus despite neither member being essential individually. In addition, we demonstrate the pNiiA-CPR strategy is suitable for in vivo phenotypic analyses, as a number of conditional mutants, including an ERG11 double mutant (erg11BDelta, pNiiA-ERG11A), failed to establish a terminal infection in an immunocompromised mouse model of systemic aspergillosis. Collectively, the pNiiA-CPR strategy enables a rapid and reliable means to directly identify, phenotypically characterize, and facilitate target-based whole cell assays to screen A. fumigatus essential genes for cognate antifungal inhibitors.     

中国大陆地区曲霉病流行现状分析

目的了解中国大陆地区曲霉病流行状况及诊治现状。方法通过CNKI及Pubmed搜索1991年来中国大陆地区曲霉病及曲霉相关文献,进行数据统计和总结。结果 1991年1月～2009年10月报道曲霉病1457例,其中481例有病原学证据,258例进行菌种鉴定,其中烟曲霉153例。感染部位最常见于肺,为1047例。病原学诊断依据主要是镜检和培养;菌种鉴定主要依赖形态学特征,仅4例进行分子生物学鉴定;仅少数进行半乳甘露聚糖及葡聚糖检测;体外药敏试验少,仅报道2株黄曲霉对两性霉素B耐药,2株烟曲霉多药耐药。伊曲康唑为侵袭性曲霉感染经验治疗(抢先治疗)的首选药物。过敏性支气管肺曲霉病则多单用糖皮质激素或联合伊曲康唑,大部分慢性及腐生型曲霉病及鼻窦曲霉病患者行手术治疗。结论中国大陆地区曲霉病流行趋势与国际一致,非烟曲霉感染有所增加,感染部位仍以肺为主。应提高菌种形态学和分子生物学鉴定水平,积极开展非培养检测手段,保证正确和及时地诊断;加强药敏监测,为临床治疗提供有效信息。     

小鼠烟曲霉角膜炎的实验研究

目的 比较伊曲康唑和氟康唑对烟曲霉的体外抗菌活性,观察伊曲康唑对小鼠烟曲霉角膜炎的治疗作用.方法 通过角膜基质注射法建立烟曲霉角膜炎小鼠模型.造模后观察角膜病变,取角膜病变处分泌物做真菌镜检、真菌培养以证实造模成功.用药基法检测伊曲康唑和氟康唑对烟曲霉的最低抑菌浓度( MIC)和最低杀菌浓度(MFC).对烟曲霉角膜炎小鼠给予伊曲康唑治疗,治疗结束行临床评分、炎性评分、菌落形成单位测定以评价疗效.结果 伊曲康唑对烟曲霉的MIC和MFC分别为6.25 μg/mL、12.5 μg/mL;氟康唑对烟曲霉的MIC和MFC分别为500 μg/mL、1 000 μg/mL.伊曲康唑治疗组临床评分、炎性评分和测定的菌落数较对照组均明显减少(P＜0.05).结论 伊曲康唑对烟曲霉的体外抗菌活性优于氟康唑,并且对烟曲霉性角膜炎有明显疗效.     

Aspergillus fumigatus causes in vitro electrophysiological and morphological modifications in human nasal epithelial cells

The role of the airway epithelium in the development of invasive aspergillosis in immunocompromised hosts has rarely been studied although patients at risk for this infection frequently have epithelial damage. We developed an in vitro model of primary culture of human nasal epithelial cells (HNEC) in air-liquid interface, which allows epithelial cell differentiation and mimics in vivo airway epithelium. We subsequently tested 7-day and 24-hour Aspergillus fumigatus filtrates on the apical side of HNEC to know whether A. fumigatus, the main species responsible for invasive aspergillosis, produces specific damage to the epithelial cells. The results were compared with those obtained with non-pathogenic filamentous fungi. Seven-day culture filtrates of A. fumigatus and Penicillium chrysogenum induced electrophysiological modifications whatever the fungus tested. In contrast, only 24-hour A. fumigatus filtrates induced a specific decrease in transepithelial resistance, hyperpolarization of the epithelium, and cytoplasmic vacuolization of HNEC compared with both A. niger and Penicillium chrysogenum. The inhibition of the A. fumigatus effects with amiloride suggests that the 24-hour fungal filtrate acts through sodium channels of HNEC. These early modifications of the epithelial cells could facilitate colonization of the airways by A. fumigatus. To know whether the molecules involved are specific to A. fumigatus or simply produced more rapidly than by other filamentous fungi warrants further investigation. In this perspective, the primary culture of HNEC represents a suitable model to study the interactions between airway epithelial cells and A. fumigatus.     

Characterization of a novel gene for strain typing reveals substructuring of Aspergillus fumigatus across North America

Fifty-five epidemiologically linked Aspergillus fumigatus isolates obtained from six nosocomial outbreaks of invasive aspergillosis were subtyped by sequencing the polymorphic region of the gene encoding a putative cell surface protein, Afu3g08990 (denoted as CSP). Comparative sequence analysis showed that genetic diversity was generated in the coding region of this gene by both tandem repeats and point mutations. Each unique sequence in an outbreak cluster was assigned an arbitrary number or CSP sequence type. The CSP typing method was able to identify "clonal" and genotypically distinct A. fumigatus isolates, and the results of this method were concordant with those of another discriminatory genotyping technique, the Afut1 restriction fragment length polymorphism typing method. The novel single-locus sequence typing (CSP typing) strategy appears to be a simple, rapid, discriminatory tool that can be readily shared across laboratories. In addition, we found that A. fumigatus isolates substructured into multiple clades; interestingly, one clade consisted of isolates predominantly representing invasive clinical isolates recovered from cardiac transplant patients from two different outbreak situations. We also found that the A. fumigatus isolate Af293, whose genome has been sequenced, possesses a CSP gene structure that is substantially different from those of the other A. fumigatus strains studied here, highlighting the need for further taxonomic study.     

Polarized response of endothelial cells to invasion by Aspergillus fumigatus

Hyphal invasion of blood vessels is a prominent feature of invasive aspergillosis. During invasive pulmonary aspergillosis, Aspergillus fumigatus hyphae invade the abluminal endothelial cell surface, whereas they invade the luminal endothelial cell surface during haematogenous dissemination. We investigated the endothelial cell response to abluminal and luminal infection with A. fumigatus hyphae in vitro . We found that these hyphae invaded the abluminal endothelial cell surface without inducing the formation of endothelial cell pseudopods. Also, the internalized hyphae were surrounded by a loose network of microfilaments. In contrast, A. fumigatus hyphae invaded the luminal endothelial cell surface by inducing by the formation of endothelial cell pseudopods. These endocytosed hyphae were surrounded by a tight network of microfilaments. Abluminal infection induced greater E-selectin, IL-8, tissue factor and TNF-α gene expression, but less endothelial cell damage than did luminal infection. Endothelial cell stimulation by infection of either surface was mediated by endothelial cell-derived TNF-α, and was not influenced by gliotoxin secreted by A. fumigatus . These differences in the endothelial cell response to abluminal versus luminal infection may contribute to differences in the pathogenesis of invasive versus haematogenously disseminated aspergillosis.     

Gene silencing with RNA interference in the human pathogenic fungus Aspergillus fumigatus

Aspergillus fumigatus is an opportunistic pathogenic fungus which causes fatal invasive aspergillosis among immunocompromised patients. To obtain a better understanding of the key elements involved in A. fumigatus virulence and to identify possible drug targets, it is necessary to be able to generate gene-deletion strains. Unfortunately, the molecular techniques available do not include a rapid method to disrupt and identify essential genes. RNA interference, a process in which the presence of double-stranded RNA homologous to a gene of interest results in specific degradation of the corresponding message, has been successfully tested on A. fumigatus. We have shown that expression of double stranded RNA corresponding to portions of the ALB1/PKSP and FKS1 genes results in reduced mRNA levels for those genes, with phenotypic consequences similar to that of gene disruption. The two genes could also be subjected to simultaneous interference through expression of chimeric double-stranded RNA. Use of RNA interference in Aspergillus will allow easier examination of the phenotypic consequences of reducing expression of a gene of interest, especially for essential genes.     

Evidence for genetic differentiation and variable recombination rates among Dutch populations of the opportunistic human pathogen Aspergillus fumigatus

As the frequency of antifungal drug resistance continues to increase, understanding the genetic structure of fungal populations, where resistant isolates have emerged and spread, is of major importance. Aspergillus fumigatus is an ubiquitously distributed fungus and the primary causative agent of invasive aspergillosis (IA), a potentially lethal infection in immunocompromised individuals. In the last few years, an increasing number of A. fumigatus isolates has evolved resistance to triazoles, the primary drugs for treating IA infections. In most isolates, this multiple-triazole-resistance (MTR) phenotype is caused by mutations in the cyp51A gene, which encodes the protein targeted by the triazoles. We investigated the genetic differentiation and reproductive mode of A. fumigatus in the Netherlands, the country where the MTR phenotype probably originated, to determine their role in facilitating the emergence and distribution of resistance genotypes. Using 20 genome-wide neutral markers, we genotyped 255 Dutch isolates including 25 isolates with the MTR phenotype. In contrast to previous reports, our results show that Dutch A. fumigatus genotypes are genetically differentiated into five distinct populations. Four of the five populations show significant linkage disequilibrium, indicative of an asexual reproductive mode, whereas the fifth population is in linkage equilibrium, indicative of a sexual reproductive mode. Notably, the observed genetic differentiation among Dutch isolates does not correlate with geography, although all isolates with the MTR phenotype nest within a single, predominantly asexual, population. These results suggest that both reproductive mode and genetic differentiation contribute to the structure of Dutch A. fumigatus populations and are probably shaping the evolutionary dynamics of drug resistance in this potentially deadly pathogen.     

Taxonomy and identification of the species involved in nosocomial aspergillosis

Although Aspergillus fumigatus is the most common etiological agent of invasive aspergillosis, other Aspergillus spp. such as A . flavus, A. niger, A. terreus and A. nidulans (Emericella nidulans) among others, have been also implicated. In this article, the taxonomy of the genus Aspergillus and the characteristics of the species most frequently isolated from patients with nosocomial aspergillosis are reviewed.     

A murine model of allergic bronchopulmonary aspergillosis with elevated eosinophils and IgE.

A model of allergic bronchopulmonary aspergillosis was developed by exposing BALB/c mice to Aspergillus fumigatus (AF) Ag. Animals immunized intranasally (i.n.) with soluble AF Ag produced low levels of serum IgE compared to animals given alum precipitated AF Ag i.p. The latter treatment also produced higher levels of serum IgG1 and AF-specific IgG1 than soluble AF given i.p. or i.n.. Blood and lung eosinophilia was detected in mice repeatedly exposed to AF by i.n. but not in the groups injected i.p. Particulate AF Ag-induced striking blood and lung eosinophilia and elevated levels of serum IgE in mice preexposed to AF Ag. The results indicate that route of inoculation and physical nature of Ag determine the immune response and can be manipulated to obtain enhanced IgE, eosinophils, or both in the animal model.     

Detection of Aspergillus fumigatus hyphae in respiratory secretions by membrane filtration, fluorescent labelling and laser scanning

The detection of Aspergillus fumigatus hyphae in bronchoalveolar lavage fluid (BAL) and sputum is diagnostically useful in patients at risk of invasive aspergillosis. We report a dedicated enzymatic-chemical sample pretreatment that allows the application of a previously described solid phase cytometry (SPC) method for detection of A. fumigatus hyphae in sputum and BAL samples. Non-specific detection of fungal hyphae by SPC is based on a 'viability' staining using carboxyfluorescein diacetate. For a specific detection of A. fumigatus hyphae by SPC, viability staining is combined with a pre-incubation at 45 degrees C, immunofluorescent labelling and microscopic recognition of the characteristic hyphal morphology. Low numbers of A. fumigatus hyphae (2-10 hyphae/sample) have now been demonstrated in spiked sputum using the non-specific and specific staining in 2.5 and 8.5 h, respectively.     

Invasive pulmonary aspergillosis due to a mixed infection caused by Aspergillus flavus and Aspergillus fumigatus

Invasive pulmonary aspergillosis is typically caused by a single Aspergillus species, most frequently Aspergillus fumigatus. Here we report that a lung transplant recipient developed invasive aspergillosis due to a mixed infection caused by Aspergillus flavus and A. fumigatus. The implications for this unusual finding are discussed.