Elastase production in clinical isolates of Aspergillus

Imaging of Sella and Parasellar Region

The sellar and parasellar region is complex, with a unique meningeal, neural, vascular, and bony anatomy. Understanding the imaging anatomy is critical for accurate imaging interpretation. resonance (MR) imaging is the primary modality for pituitary imaging, whereas computed tomography may be used when MR imaging is contraindicated, and provides complementary bony anatomic information. This article reviews embryology and anatomy of the sellar and parasellar region. Imaging appearances of pituitary adenomas, Rathke cleft cysts, meningiomas, craniopharyngiomas, arachnoid cysts, vascular disorders, infectious abnormalities, and pituitary apoplexy are discussed and illustrated.

[Studies on Elastase and Elastase Inhibitor from Aspergillus flavus]

The biological properties of elastase and Aspergillus flavus elastase inhibitor (AFLEI) from A. flavus were examined. Pathogenicity of elastase was investigated in mice immunocompromised with cyclophosphamide, cyclosporine, prednisolone and carrageenan. Compared to cyclophosphamide immunocompromised mice treated with the spores of elastase nonproducing strain, cyclophosphamide immunocompromised mice treated with the spores of elastase producing strain had a significantly shorter survival rate. Molecular mass of AFLEI was determined to be 7525.8 Da. The elastolytic activity of elastases from A. flavus, and human leukocytes were inhibited by AFLEI. The primary structure of AFLEI was determined by the Edman sequencing procedure. The search for amino acid homology with other proteins demonstrated that amino acid residues 1 to 68 of AFLEI are 100% identical to residues 20 to 87 of the hypothetical protein AFUA_3G14940 of A. fumigatus. When immunocompromised mice administered of cyclophosphamide were infected by inhalation of A. flavus then administered amphotericin B (AMPH) alone or in combination with AFLEI, survival rate tended to be higher with combination treatment than with AMPH alone. Moreover, although extensive bleeding was seen in pathology sections taken from rat lung resected 24 h after elastase was administered to the lung via the bronchus, this bleeding was inhibited by AFLEI. The X-ray analysis has revealed that the structure of this inhibitor was wedge shaped and composed of a binding loop and a scaffold protein core. As synthetic-inhibitor strongly inhibited cytotoxicity induced by elastase in human-derived cells, it could prove beneficial for the treatment of pulmonary aspergillosis.

Clinical manifestations, diagnosis, and treatment outcome of CNS aspergillosis: A systematic review of 235 cases

Aspergillus is a ubiquitous ascomycete that can cause a variety of clinical presentations depending on immune status. Central nervous system aspergillosis is a fatal disease with non-specific clinical features. The aim of this systematic review was to evaluate the epidemiology, clinical features, diagnosis and therapeutic interventions in CNS aspergillosis patients. We also aimed to examine the possible predictors of mortality in neuroaspergillosis. Literature search was performed in Medline, PubMed, and Google scholar and all patients≥18 years with proven CNS aspergillosis were included. A total of 175 articles (235 patients) were included in the final analysis. Their mean age was 51 years and the majority were male (57.4%). Overall case-fatality was 45.1%. Aspergillus fumigatus was the most common species (70.8%) followed by A. flavus (18.6%). Corticosteroids (22.6%), malignancy (19.1%) and diabetes mellitus (14%) were the most common risk factors. Neuroimaging findings included cerebral abscess (70.2%), meningitis (14%), infarction (13.2%) and mycotic aneurysm (8.9%). Disseminated disease (29.2% vs 17.8%, p 0.03), CSF hypoglycorrhachia (48.1% vs 22.2%, P: 0.001) and heightened CSF galactomannan (3.62 vs 2.0ng/ml, p 0.05), were the factors associated with poor outcome in neuroaspergillosis. Persons infected with Aspergillus flavus (13.1% vs 3.1%, P: 0.01), and having been treated with Voriconazole (51.9% vs 29.2%, P: 0.004) were more likely to survive. Our review will provide insight into the different spectrums of CNS aspergillosis. Notwithstanding the promising role of Voriconazole, future work is required to ascertain the role of combination antifungal therapy.

Influence of Severity of Type and Timing of Retrospectively Reported Childhood Maltreatment on Female Amygdala and Hippocampal Volume

Deleterious effects of adverse childhood experiences (ACE) on human brain volume are widely reported. First evidence points to differential effects of ACE on brain volume in terms of timing of ACE. Upcoming studies additionally point towards the impact of different types (i.e., neglect and abuse) of ACE in terms of timing. The current study aimed to investigate the correlation between retrospectively reported severity of type (i.e., the extent to which subjects were exposed to abuse and/or neglect, respectively) and timing of ACE on female brain volume in a sample of prolonged traumatized subjects. A female sample with ACE (N = 68) underwent structural magnetic resonance imaging and a structured interview exploring the severity of ACE from age 3 up to 17 using the “Maltreatment and Abuse Chronology of Exposure” (MACE). Random forest regression with conditional interference trees was applied to assess the impact of ACE severity as well as the severity of ACE type, (i.e. to what extent individuals were exposed to neglect and/or abuse) at certain ages on pre-defined regions of interest such as the amygdala, hippocampus, and anterior cingulate (ACC) volume. Analyses revealed differential type and timing-specific effects of ACE on stress sensitive brain structures: Amygdala and hippocampal volume were affected by ACE severity during a period covering preadolescence and early adolescence. Crucially, this effect was driven by the severity of neglect.

Evaluation of in vitro activities of extracellular enzymes from Aspergillus species isolated from corneal ulcer/keratitis

Mycotic/fungal keratitis is a suppurative, generally ulcerative infection of the cornea. The filamentous fungi, Aspergillus spp. are the second leading cause of mycotic keratitis, particularly in India. Aspergillus spp. produce a range of extracellular enzymes that are used to break down complex molecules and used for growth and reproduction, also for survival on/in host organism. The current study was designed with an objective to screen in vitro extracellular enzyme activity of Fusarium and Aspergillus isolates from mycotic keratitis patients and to correlate the same as a putative virulence factor. Extracellular enzymes viz., deoxyribonuclease (DNase), protease, lipase, elastase, keratinase, etc., produced by Aspergillus have key role in keratomycosis and hence their (n = 85) in vitro activities were investigated. It was found that, the majority of the Aspergillus isolates produced protease (n = 75; 88% of 85) followed by lipase (n = 59; 69% of 85), DNase (n = 35; 41% of 85), elastase (n = 26; 31% of 85) and keratinase (n = 13; 15% of 85). The enzyme activity indices (EAI) for DNase, elastase, protease and lipase ranged between 1.01 and 1.98, whereas elastase EAI varied between 1.26 and 1.92. DNase, protease and lipase showed a maximum EAI of 1.98 and lowest EAI value of 1.01, respectively. Extracellular enzymes of Aspergillus spp. may have potential role in the onset and progression of keratitis.

Detection of virulence factors and antifungal susceptibility of human and avian Aspergillusflavus isolates

Aspergillusflavus is the second leading cause of invasive and non-invasive aspergillosis. Secretion of hydrolytic enzymes is considered as a virulence factor in this species. Our work aimed to study in vitro production of some virulence factors, to evaluate the biofilm production against human and avian A. flavus isolates and to investigate the antifungal susceptibility agents. Hydrolytic enzymes, biofilm production and molecular typing were studied for 62 human and 36 avian A. flavus isolates by specific solid media and six microsatellite markers. The susceptibility to antifungal agents was evaluated for 37 human isolates. All human and avian A. flavus isolates showed positive activities of extracellular hydrolase: phospholipase, protease and hemolysin. A positive elastase activity was seen in 64.51% of human A. flavus isolates and 86.1% of avian A. flavus isolates. All A. flavus in these two populations formed biofilms. Statistical significant difference was observed for the mean phospholipase activities (P=0.025) and biofilm quantification (P=0.0001) between human and avian A. flavus isolates. The in vitro susceptibility results showed a resistance in 83.7%, 81.08% and 16.21% of A. flavus isolates respectively to amphotericin B, itraconazole and posaconazole. No association was noted between all virulence factors and the genotypes of human and avian isolates. Our study allowed us to show that human strains have a higher production of extracellular hydrolases and biofilm then avian strains. These virulence factors appear to act synergistically to contribute to the virulence of A. flavus strains. Moreover, significant correlation between virulence patterns and antifungal susceptibility profiles was observed.

Murine model of invasive pulmonary Aspergillosis: Follow-up of tissue injury, fungal burden and mortality with distinct elastase production strains

To study invasive pulmonary Aspergillosis (IPA), we depleted neutrophils in mice using the monoclonal antibody anti-Gr-1/Ly-6G. Immunocompetent and neutropenic mice were infected via intratracheal with conidia of Aspergillus fumigatus clinical isolates, characterized as either higher or lower elastase producers. Neutropenic animals exhibited 100% mortality in 5 days, for both strains, and were observed survival curves overlapped, lungs with angioinvasion, rupture of bronchial and vascular walls, associated with exuberance of conidia filamentation. The immunocompetent animals infected with the lower elastase producer strain presented with upregulated inflammatory processes, and a lack of conidia filamentation in the tissue. The fungal burden in the lungs was not different in the immunocompetent and neutropenic groups. These findings confirm the protective role of neutrophils against A. fumigatus and suggest that the fungal elastinolytic activity is not a critical virulence factor but may be involved in tissue injury.

Aspergillus flavus: an emerging non-fumigatus Aspergillus species of significance

Invasive aspergillosis is rare in immunocompetent people but contributes to significant morbidity and mortality in immunosuppressed patients. The majority (approximately 80%) of invasive Aspergillus infections is caused by Aspergillus fumigatus. The second most frequent (approximately 15-20%) pathogenic species is Aspergillus flavus and to a lesser extent, Aspergillus niger and Aspergillus terreus. Aspergillus flavus has emerged as a predominant pathogen in patients with fungal sinusitis and fungal keratitis in several institutions worldwide. To date, there has not been any publication exclusively reviewing the topic of A. flavus in the literature. This article reviews the microbiology, toxigenicity and epidemiology of A. flavus as well as describes the clinical characteristics, diagnosis and management of infections caused by this organism.

Investigation of extracellular elastase, acid proteinase and phospholipase activities as putative virulence factors in clinical isolates of Aspergillus species

We investigated the production of extracellular elastase, acid proteinase and phospholipase enzyme activities in clinical isolates of Aspergillus fumigatus, Aspergillus flavus and Aspergillus niger and any possible correlation between the existence of these enzymes and development of invasive aspergillosis. A total of 73 strains (45 A. fumigatus, 23 A. flavus, 5 A. niger) isolated from patients with invasive aspergillosis (n = 55), superficial aspergillosis (n = 5), allergic bronchopulmonary aspergillosis (n = 1), and from those colonized with Aspergillus (n = 12) were included in the study. The enzymatic activities were tested on solid media supplemented with the corresponding substrates. Elastase activity was detected in 95.6, 82.6, and 0% of A. fumigatus, A. flavus, and A. niger isolates, respectively. Acid proteinase activity was detected only for A. fumigatus and in 20 of 45 isolates belonging to this species. Phospholipase activity was present in all strains of A. fumigatus and A. niger but in none of the isolates of A. flavus. No statistical correlation could be established between the existence of elastase or acid proteinase activity and development of invasive disease (p > 0.05). While high phospholipase production was found to be associated with development of invasive aspergillosis (p < 0.01), not all isolates that caused invasive diseases showed high phospholipase activities.

Intracranial mycotic aneurysm due to Aspergillus species

BACKGROUND

Intracranial true mycotic aneurysms are uncommon and usually fatal. We report two patients with basilar mycotic aneurysms due to Aspergillus species following surgical interventions. Both patients had subarachnoid hemorrhage and diagnosis was made at autopsy only. The literature regarding etiology, clinical presentation, predisposing conditions and outcome of intracranial true mycotic aneurysms is reviewed from 1990-2005. A high index of clinical suspicion with prompt diagnosis and early treatment may improve patient outcome.

Cambios en la actividad elastasa y la capacidad colonizadora de Aspergillus fumigatus tras inoculaciones sucesivas en ratones

In a previous work we demonstrated a clear link between elastase activity and pathogenicity using what we have named the Elastase Activity Index (EAI). In the present study we have evaluated the possible variability of this index as a consequence of successive inoculations in mice. Two strains of Aspergillus fumigatus isolated from the environment without elastase activity were used. These strains were inoculated into successive batches of ten mice. Our results showed that with each inoculation there was an increase in the number of mice on each batch from which the strain could be isolated and an increase in the number of strains with an EAI>1. This study suggests that A. fumigatus could adapt to the environment in which it is developed, increasing its pathogenic capabilities from host to host.

fos-1, a putative histidine kinase as a virulence factor for systemic aspergillosis

In fungi, two-component histidine kinases have various functions including regulation of osmosensitivity, and of cell-wall assembly. Furthermore, one of these proteins, cos-1, has been shown to be important for virulence of Candida albicans. Recently, a putative histidine kinase, fos-1, has been isolated and partially characterized from Aspergillus fumigatus. Here we compare the virulence of a fos-1 deletion strain with that of the parental wild-type strain in a murine model of systemic aspergillosis. Our results show that the fos-1 deletion strain has significantly reduced virulence as compared with the parental wild-type strain. Thus, we propose that the fos-1 two-component histidine kinase is a virulence factor of A. fumigatus.

Correlation between the elastase activity index and invasiveness of clinical isolates of Aspergillus fumigatus

We calculated an elastase activity index (EAI) by dividing the diameter of the elastin lysis halo by the fungal growth diameter. After 10 days' incubation at 37 degrees C, all strains but one obtained from invasive aspergillosis showed an EAI > or = 1. Of the 18 strains obtained from colonized patients, only 4 (22.2%) had an EAI > or = 1, whereas neither of the strains isolated from patients with fungus ball reached this value. Overall, 44 out of the 142 strains obtained from the environment had an EAI > or = 1 (30.9%).

Putative virulence factors of Aspergillus fumigatus

Various putative virulence factors of Aspergillus fumigatus have been studied over the past decades. A. fumigatus gliotoxin is a potent inhibitor of the mucociliary system. Several fungal metabolites interfere with phagocytosis and opsonization including toxins, 'conidial inhibitory factor', 'A. fumigatus diffusible product' and 'complement inhibitory factor'. A. fumigatus can bind specifically to different host tissues components, whereas toxins give a general and significant immunosuppressive effect on host defences. Circumstantial evidence links the production of elastinolytic proteases with the ability to cause disease. However, none of the reports demonstrates conclusively a decisive role for any of the virulence factors described thus far. It is conceivable that proteolytic enzyme activities such as those expressed by AFAlp are one of a number of factors, each with a minor effect, that combine to facilitate disease progression.

Lack of host specialization in Aspergillus flavus

Aspergillus spp. cause disease in a broad range of organisms, but it is unknown if strains are specialized for particular hosts. We evaluated isolates of Aspergillus flavus, Aspergillus fumigatus, and Aspergillus nidulans for their ability to infect bean leaves, corn kernels, and insects (Galleria mellonella). Strains of A. flavus did not affect nonwounded bean leaves, corn kernels, or insects at 22 degrees C, but they killed insects following hemocoelic challenge and caused symptoms ranging from moderate to severe in corn kernels and bean leaves injured during inoculation. The pectinase P2c, implicated in aggressive colonization of cotton balls, is produced by most A. flavus isolates, but its absence did not prevent colonization of bean leaves. Proteases have been implicated in colonization of animal hosts. All A. flavus strains produced very similar patterns of protease isozymes when cultured on horse lung polymers. Quantitative differences in protease levels did not correlate with the ability to colonize insects. In contrast to A. flavus, strains of A. nidulans and A. fumigatus could not invade living insect or plant tissues or resist digestion by insect hemocytes. Our results indicate that A. flavus has parasitic attributes that are lacking in A. fumigatus and A. nidulans but that individual strains of A. flavus are not specialized to particular hosts.

Aspergillus fumigatus and aspergillosis

Aspergillus fumigatus is one of the most ubiquitous of the airborne saprophytic fungi. Humans and animals constantly inhale numerous conidia of this fungus. The conidia are normally eliminated in the immunocompetent host by innate immune mechanisms, and aspergilloma and allergic bronchopulmonary aspergillosis, uncommon clinical syndromes, are the only infections observed in such hosts. Thus, A. fumigatus was considered for years to be a weak pathogen. With increases in the number of immunosuppressed patients, however, there has been a dramatic increase in severe and usually fatal invasive aspergillosis, now the most common mold infection worldwide. In this review, the focus is on the biology of A. fumigatus and the diseases it causes. Included are discussions of (i) genomic and molecular characterization of the organism, (ii) clinical and laboratory methods available for the diagnosis of aspergillosis in immunocompetent and immunocompromised hosts, (iii) identification of host and fungal factors that play a role in the establishment of the fungus in vivo, and (iv) problems associated with antifungal therapy.

Murine macrophage elastolytic activity induced by Aspergillus fumigatusstrains in vitro: evidence of the expression of two macrophage-induced protease genes

The interaction between Aspergillus fumigatus conidia and murine macrophages of various origins was investigated. Cocultures were carried out between A. fumigatus strains and freshly isolated murine pulmonary alveolar macrophages or two murine macrophage cell-lines: murine alveolar cell-line MALU and murine astrocytoma cell-line J774. By measuring the variation of elastolytic activity in the coculture supernatants with two elastin substrates, we demonstrated that either viable or fixed A. fumigatus or C. albicans yeasts or nonspecific particles induced significant macrophage elastolytic activity. The effect of A. fumigatus supernatant or the purified A. fumigatus galactomannan suggested also the possible involvement of this polysaccharide in macrophage-protease gene expression, release, and activity in invasive aspergillosis. The effect of inhibitory compounds demonstrated the potential implication of a macrophagic metalloprotease and a macrophagic cysteine protease. RNA analysis allowed us to demonstrate the induction of expression of two macrophagic protease genes in stimulated macrophages. Two distinctive mechanisms appeared to be implicated in macrophage protease induction: nonspecific phagocytosis in the earliest times of the coculture and (or) specific galactomannan recognition after its gradual release by the mycelium.

Virulence factors of medically important fungi

Human fungal pathogens have become an increasingly important medical problem with the explosion in the number of immunocompromised patients as a result of cancer, steroid therapy, chemotherapy, and AIDS. Additionally, the globalization of travel and expansion of humankind into previously undisturbed habitats have led to the reemergence of old fungi and new exposure to previously undescribed fungi. Until recently, relatively little was known about virulence factors for the medically important fungi. With the advent of molecular genetics, rapid progress has now been made in understanding the basis of pathogenicity for organisms such as Aspergillus species and Cryptococcus neoformans. The twin technologies of genetic transformation and "knockout" deletion construction allowed for genetic tests of virulence factors in these organisms. Such knowledge will prove invaluable for the rational design of antifungal therapies. Putative virulence factors and attributes are reviewed for Aspergillus species, C. neoformans, the dimorphic fungal pathogens, and others, with a focus upon a molecular genetic approach. Candida species are excluded from coverage, having been the subject of numerous recent reviews. This growing body of knowledge about fungal pathogens and their virulence factors will significantly aid efforts to treat the serious diseases they cause.

Disruption of the serine proteinase gene (sep) in Aspergillus flavus leads to a compensatory increase in the expression of a metalloproteinase gene (mep20)

The serine proteinase gene (sep) in Aspergillus flavus was disrupted by homologous recombination with a hygromycin resistance gene as the marker. The gene-disrupted mutant GR-2 contained a single-copy insertion of the marker gene and did not express the sep gene. Serine proteinase activity, 36-kDa protein labeled by 3H-diisopropylfluorophosphate, and immunologically detectable proteinase were not detected in the culture fluid of GR-2. Despite the absence of the serine proteinase, the total elastinolytic activity levels in the mutant and the wild-type A.flavus were comparable. Immunoblots revealed that the mutant secreted greater amounts of an elastinolytic metalloproteinase gene (mep20) product than did the wild type. Furthermore, mep20 mRNA levels, measured by RNase protection assay, in the mutant were higher than those in the wild type. Inhibition of the serine proteinase by Streptomyces subtilisin inhibitor (SSI) in the culture medium of wild-type A.flavus also resulted in an elevation of mep20 gene products. Although no serine proteinase activity could be detected, the level of elastinolytic activity of the SSI-treated culture was comparable to that of the control. Immunoblots revealed that the addition of SSI caused an elevation in the levels of metalloproteinase and its mRNA. These results suggest that the expression of the genes encoding serine and metalloproteinases are controlled by a common regulatory system and the fungus has a mechanism to sense the status of extracellular proteolytic activities.

Expression of PZ-peptidases by cultures of several pathogenic fungi. Purification and characterization of a collagenase from Trichophyton schoenleinii

Peptidolytic activity was studied in the broken-cell extracts of 17 isolates of pathogenic fungi tested with phenylazobenzyloxycarbonyl-Pro-Leu-Gly-Pro-Arg (PZ-PLGPA) as a substrate. All the fungi studied except Candida spp., Cryptococcus neoformans and two actinomycetes hydrolyzed the substrate and therefore contained a so-called PZ-peptidase activity. Of all the positive strains, Trichophyton schoenleinii, a pathogenic fungus showed the highest activity and was therefore chosen as a source for PZ-peptidase purification. The four chromatographic steps, a 'negative' dye column, a 'positive' dye column, hydroxyapatite Ultrogel, and modified TSK (HW 55), gave a highly purified peptidase with a 12% overall yield. Inhibitor studies suggested that the 82 000 M(r) PZ-peptidase is a metalloproteinase. Moreover it cleaved native rat type I collagen. Partial peptide sequencing showed a strong sequence homology to regions of two metalloproteinases previously identified in the yeast Saccharomyces cerevisiae and in rat.

HN, Holden DW. Regulation of fungal extracellular proteases and their role in mammalian pathogenesis

Fungal infection in the immunocompromised host is a problem of increasing importance. The virulence determinants of Aspergillus fumigatus, the major agent of invasive aspergillosis, and of Candida albicans, causing candidiasis, are not well characterized. For both pathogens, the involvement of extracellular proteases in pathogenesis is discussed. The use of gene disruption techniques to inactivate the A. fumigatus alkaline protease and metalloprotease genes has led to the firm conclusion that neither of these enzymes has a significant role in virulence. The diploid nature of C. albicans (necessitating sequential inactivation of both alleles for gene disruption studies) and the presence of a multigene family encoding secreted aspartyl proteases has hampered progress in understanding the role of proteases in virulence. We discuss the involvement of wide-domain regulators in the control of protease production and give an example of how one of these regulators (encoded by the areA gene) has been used in virulence studies. Key words: Aspergillus, Candida, proteases, gene regulation.

Aspergillusproteinases and their interactions with host tissues

Invasive aspergillosis is a life-threatening infection that is caused primarily by the species Aspergillus fumigatus and A. flavus, both of which are highly angioinvasive. From this observation, interest has focused on proteinases produced by these organisms and their possible roles in the pathogenesis of infection. Both species produce alkaline serine proteinases (ALP) and metalloproteinases during the course of infection based on immunohistochemistry of experimental lesions and serologic response of patients. These enzymes can be shown to degrade numerous biologically relevant targets, including elastin, collagen, laminin, fibrinogen, and iC3b. Physicochemical properties, immunoreactivities, and amino acid sequences of the ALP of A. fumigatus and A. flavus show that these two enzymes are closely related. The metalloproteinases, however, appear to represent members of a small family of similar enzymes. Finally, although studies using conventionally produced mutants support roles for these hydrolases as virulence factors in aspergillosis, similar studies using strains of A. fumigatus in which the enzymatic activity has been ablated through gene disruption do not reveal differences in virulence between the wild-type strains and the mutants. Key words: aspergillosis, proteinase, pathogenesis.

Cloning and characterization of the cDNAs and genes (mep20) encoding homologous metalloproteinases from Aspergillus flavus and A. fumigatus

Aspergillus fumigatus (Afu) and A. flavus (Afl), two causative agents of invasive aspergillosis, produce highly homologous serine proteinases. In addition, the former produces a 42-kDa metalloproteinase (MEP), whereas the latter produces a 23-kDa MEP. The cDNA and the gene encoding the 42-kDa MEP were cloned and sequenced. Here, we report the cloning of the cDNA and the gene encoding the 23-kDa MEP from Afl and a homologous gene from the Afu. Using degenerate primers based on the amino acid (aa) sequence of A. oryzae (Ao) MEP and thermolysin-like proteinases, a 282-bp fragment of the 23-kDa MEP-encoding gene of Afl was cloned by PCR. A 6.5-kb KpnI fragment of Afl genomic DNA containing the complete gene was cloned. The open reading frame (ORF) in this gene encodes a protein of 381 aa. Since the mature enzyme from this and other aspergilli would have a theoretical molecular mass of about 20 kDa, this MEP-encoding gene is designated mep20. A Western blot of the protein in the culture filtrate of Afl with polyclonal antibodies prepared against the MEP showed a single band at 23 kDa. The N-terminal sequence of the extracellular MEP20, TKVAS, was found at aa 194-198 within the ORF. Thus, the primary translation product has a putative 19-aa signal and a pro region of 174 aa. A homologous gene cloned from a genomic DNA library of Afu showed an ORF encoding 365 aa. Comparison of the nucleotide (nt) sequences of the cDNAs cloned by RT-PCR with their respective genes showed that there are no introns in the ORF of mep20 in Afl, but there is a 59-bp intron in the gene from Afu. The MEP20 of Afl and Afu have 68% identity and show weak immunological cross reactivity. MEP20 from both these fungi share about 60% sequence identity with the penicillolysin of Penicillium citrinum and the neutral protease II of Ao. MEP20 of Afl and Afu show only the conserved sequence, HEFTHA, but not the two other conserved sequences seen in thermolysins and similar MEP.

Expression of elastinolytic activity among isolates in Aspergillus section flavi

A survey of the distribution of elastinolytic potential among 32 culture collection isolates of Aspergillus flavus. A. oryzae, A. parasiticus, A. sojae, A. nomius, and A. tamarii revealed this character to be highly conserved within Aspergillus Section Flavi. Furthermore, 144 isolates of A. flavus from environmental samples from six separate regions of the United States produced elastase on solid medium. Most previously described polymorphisms in elastinolytic potential were attributed to the toxicity of borate buffers. Replacement of borate with HEPES (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) resulted in detection of elastase production on solid medium by all tested fungal isolates except two that had been in culture over 50 years. In liquid culture, only isolates of A. flavus, A. tamarii, and A. oryzae accumulated elastase activity. Although isoelectric focusing revealed only one isoform (pI 9.0) of elastase in these culture filtrates, elastinolytic activity in filtrates was partially inhibited by both 1,10-phenanthrolene (2 mM) and phenylmethylsulfonylfluoride (2 mM), suggesting the presence of both metallo and serine elastinolytic proteinases.

The role of bacterial proteases in the pathogenesis of cystic fibrosis

Among the roles of mediators damaging the respiratory epithelium in patients with cystic fibrosis (CF) during the course of chronic, purulent bronchitis, that of neutrophil proteases is well established. The role of bacterial proteases is less well known. Among all pathogens colonizing the airways in CF, Pseudomonas aeruginosa is quantitatively the dominant pathogen; Staphylococcus aureus and Haemophilus influenzae are present in lower numbers. Anaerobic bacteria may be detected in numbers exceeding those of Staphylococcus aureus and Haemophilus influenzae. Among all enzymes secreted by these bacterial strains, Pseudomonas elastase and alkaline protease were shown to be secreted in vivo over prolonged periods in the airways. These enzymes, mainly elastase, have proteolytic activity on many proteins involved in host defense mechanisms, often the same as those hydrolyzed by neutrophil proteases. Pseudomonas elastase has damaging effects on the respiratory epithelium; it has recently also been shown to augment the permeability of the respiratory epithelium cultured in vitro by proteolytic attack of tight junctions. The potential role of proteases and other enzymes secreted by anaerobic bacteria has not been studied in this disease. In conclusion, bacterial proteases secreted in vivo may play a role in the pathogenesis of the airway disease in CF; their relative importance to the role of host proteases is, however, often difficult to determine.

Purification and characterization of an elastinolytic metalloprotease from Aspergillus fumigatus and immunoelectron microscopic evidence of secretion of this enzyme by the fungus invading the murine lung

Extracellular proteases have been suggested to be virulence factors in invasive aspergillosis. Since serine protease gene-disrupted mutants retain virulence, other proteases are suspected to be also involved in the degradation of lung structural material. An elastinolytic neutral metalloprotease was purified 320-fold from the extracellular fluid of Aspergillus fumigatus grown on elastin by affinity chromatography on bacitracin-Sepharose 4B and gel filtration on Sephadex G-75. The molecular mass was determined to be 43 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. No carbohydrate was attached to this metalloprotease, and its first 22 N-terminal amino acids did not show any homology with the known metalloproteases. The enzyme was completely inhibited by EDTA, 1,10-phenanthroline, and phosphoramidon but not by inhibitors specific for serine, aspartate, and cysteine proteases. Zn2+ and, to a lesser extent, Co2+ reversed the inhibition caused by 1,10-phenanthroline. The protease hydrolyzed the peptide bonds His-Leu, Ala-Leu, Tyr-Leu, Gly-Phe, and Phe-Phe in the B chain of insulin. Synthetic substrate Abz-Ala-Ala-Phe-Phe-pNA could be used for the fluorimetric assay of the A. fumigatus metalloprotease. This enzyme had maximum activity in the pH range 7.5 to 8.0 and at 60 degrees C. It retained 50% of the protease activity when held at 60 degrees C for 1 h. Zn2+ and Co2+ at 1 mM did not inhibit the protease activity. The metalloprotease was able to hydrolyze elastin, and its elastinolytic activity was comparable to that of the serine protease from this organism. The presence of Zn2+ in the culture medium stimulated the metalloprotease production. Rabbit antibodies prepared against the enzyme severely inhibited the enzyme activity. Immunogold electron microscopy revealed that A. fumigatus invading neutropenic mouse lungs secretes this metalloprotease.

Recombinant expression and antigenic properties of a 32-kilodalton extracellular alkaline protease, representing a possible virulence factor from Aspergillus fumigatus

A 32-kDa nonglycosylated alkaline protease (EC 3.4.1.14) with elastolytic activity, secreted by the opportunistic pathogen Aspergillus fumigatus ATCC 42202, is suggested to be a virulence factor of this fungus. The enzyme is a serine protease of the subtilisin family, and its cDNA nucleotide sequence has recently been reported. We have cloned the cDNA encoding the mature protease into a high-level Escherichia coli expression plasmid and produced the recombinant protease as a fusion protein with a six-adjacent-histidine affinity tag at the carboxy terminus. Subsequently, the recombinant protease was purified to homogeneity, with affinity chromatography yielding 30 to 40 mg of recombinant protease per liter of E. coli culture. Refolded recombinant protease, in comparison with native protease, demonstrated weak enzymatic activity but similar immunochemical characteristics as analyzed by antigen-specific enzyme-linked immunosorbent assay (ELISA), competition ELISA, and immunoblotting assays. To assess the allergenic potential of the protease, sera from patients with allergic bronchopulmonary aspergillosis and sera from healthy control individuals were analyzed by ELISA and immunoblotting techniques. Sera from patients with allergic bronchopulmonary aspergillosis did not have protease-specific immunoglobulin E (IgE) antibodies and, remarkably, did not show significantly elevated protease-specific IgG antibody levels compared with those in sera from healthy control individuals. This suggests that the alkaline protease from A. fumigatus does not elicit IgE antibodies and has weak immunogenicity, a property which may explain fungus persistence in allergic individuals.

Molecular genetics of Aspergillus pathogenicity

Aspergillus fumigatus is the most frequent cause of Invasive Pulmonary Aspergillosis (IPA), a life-threatening disease of immunosuppressed patients. In addition to a number of general physiological attributes of this fungus, it has been suggested that extracellular elastase and toxins might facilitate its growth in lung tissue. We have investigated the roles of two extracellular proteins, an alkaline protease with elastase activity (AFAlp), and the ribotoxin restrictocin in murine models of IPA. Gene disruption was used to create stable null mutant strains of the fungus lacking one or other protein, and their virulence and histopathological features were compared with an isogenic parental strain in steroid-treated and neutropenic mice. We have been unable to demonstrate any significant differences between the three strains, which shows that, considered independently, these proteins are not important virulence determinants. We are also interested in identifying fungal-specific gene products involved in general metabolism and which are required for growth in the lung, because these could represent new targets for antifungal drugs. For this work a model of murine IPA involving Aspergillus nidulans was established, to take advantage of the many well characterised mutations affecting metabolic pathways. Pathogenicity tests with strains carrying one of two auxotrophic mutations, lysA2 and pabaA1, have shown while lysine biosynthesis is not essential for the fungus to cause pulmonary disease, biosynthesis of p-aminobenzoic acid is essential. We are now in the process of cloning the A. fumigatus pabaA homologue to determine its function and whether this gene is required for growth of the clinically important species in the lung.

Western blot detection of IgG anti-Aspergillus fumigatus elastase in sera of patients with aspergillosis

Anti-Aspergillus fumigatus alkaline protease IgG was investigated by Western blot. Specific IgG antibodies were detected in sera of two of nine patients with proven or highly probable invasive aspergillosis and in sera of one of eight patients with proven or highly probable allergic bronchopulmonary aspergillosis. No response was obtained in sera of 23 control patients. The specific but transient IgG response to this induced enzyme does not recommend its use as sole serodiagnostic aid.

Extracellular fibrinogenolytic enzyme of Aspergillus fumigatus: substrate-dependent variations in the proteinase synthesis and characterization of the enzyme

To get a better understanding of the role of the previously reported fibrinogenolytic enzyme of Aspergillus fumigatus, we investigated the in vitro conditions of enzyme synthesis and attempted to characterize it. Modification of the nitrogen source did not influence the extracellular serine-proteinase profile, but resulted in important quantitative differences in the yields in batch cultures. The enzyme synthesis appeared to be an inducible phenomenon in A. fumigatus since it was initiated exclusively in the presence of proteins or protein hydrolysate. Free amino acids or inorganic nitrogen compounds could not promote significant enzyme production. Moreover, peptone at a concentration of 0.1% appeared to be the best inducer of enzyme synthesis. Conversely, modification of the carbon source did not affect fungal growth or enzyme synthesis. However, the production of chymotrypsin was highly sensitive to the carbohydrate level in the culture medium and, with peptone as nitrogen source, highest yields were obtained in the presence of 0.3 or 0.5% glucose. Culture filtrates of A. fumigatus CBS 113.26 grown with peptone or nitrate as nitrogen source were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Comparison of the protein patterns suggested for the proteinase a molecular mass of 33 kDa which was confirmed by chromatographic purification of the enzyme through (N alpha-CBZ)-D-phenylalanine agarose.

Evidence for possible involvement of an elastolytic serine protease in aspergillosis

A number of isolates of Aspergillus fumigatus obtained from the hospital environment produced extracellular elastolytic activity. This activity was found to be catalyzed by a single 33-kDa protein which was purified and characterized to be a serine protease. A. fumigatus, when grown on the insoluble structural material obtained from murine and bovine lung, produced the same extracellular 33-kDa elastolytic protease, indicating that this enzyme is likely to be produced when the organism infects the lung. Polymerase chain reaction with an oligonucleotide primer based on the N-terminal amino acid sequence of the elastolytic enzyme yielded a cDNA which was cloned and sequenced. The active serine motif showed more similarity to subtilisin than to mammalian elastase. The amino acid sequence showed 80% identity to the alkaline protease from Aspergillus oryzae. Screening of hospital isolates of Aspergillus flavus showed great variation in the production of elastolytic activity and a much lower level of activity than that produced by A. fumigatus. The elastolytic protease from A. flavus was shown to be a serine protease susceptible to modification and inactivation by active serine and histidine-directed reagents. This protease cross-reacted with the antibodies prepared against the elastolytic protease from A. fumigatus. Immunogold localization of the elastolytic enzyme showed that A. fumigatus germinating and penetrating into the lungs of neutropenic mice secreted the elastolytic protease. An elastase-deficient mutant generated from a highly virulent isolate of A. fumigatus caused drastically reduced mortality when nasally introduced into the lung of neutropenic mice. All of the evidence suggests that extracellular elastolytic protease is a significant virulence factor in invasive aspergillosis.

The alkaline protease of Aspergillus fumigatus is not a virulence determinant in two murine models of invasive pulmonary aspergillosis

Little is known of the pathophysiology of invasive pulmonary aspergillosis (IPA), an opportunistic fungal infection usually caused by Aspergillus fumigatus. It has been suggested that the ability of the fungus to degrade elastin may aid its invasion and growth in lung tissue. We have described previously the construction of a strain of A. fumigatus in which the gene encoding an alkaline protease, AFAlp, had been disrupted (C.M. Tang, J. Cohen, and D.W. Holden, Mol. Microbiol. 6:1663-1671, 1992); this mutant is deficient in extracellular proteolytic and elastinolytic activity over a broad pH range. In this study, we compared the pathogenicity of this and another AFAlp disruptant with their isogenic, elastase-producing parental strains in two murine models of IPA. In both models, animals were inoculated via the respiratory tract. In the first model, the inoculum was delivered as airborne conidia and animals developed signs of respiratory distress within 2 to 4 days. In the second model, conidia were administered intranasally as a suspension and the disease developed over a 2-week period. No difference was observed between the wild-type and AFAlp disruptants in terms of mortality, and elastin breakdown was detected in lung tissue from animals inoculated with all four strains. We conclude that AFAlp is not a virulence determinant in these models of IPA.

Lack of vessel wall elastolysis in human invasive pulmonary aspergillosis

In experimental studies, the apparent ability of Aspergillus fumigatus isolates to produce elastase in agar plates correlates with their ability to cause invasive pulmonary aspergillosis in mice pretreated with cortisone. Thus, elastase production may govern the pathogenicity of particular isolates. If this is so, then disruption of the elastic layers within blood vessel walls in invasive aspergillosis would be expected. To test this hypothesis, tissue blocks were prepared from nine patients with invasive pulmonary aspergillosis. Separate but immediately adjacent histological sections were stained by the Grocott and periodic acid-Schiff methods for fungal hyphae and by the elastic van Gieson technique for elastic tissue. Comparison of those segments of vessel walls infiltrated by hyphae with those not infiltrated by hyphae showed no overall loss of elastic tissue. Material from five of the cases was also stained with an unconventional combination of histochemical stains, allowing accurate identification of both fungal hyphae and elastic laminae in the same histological sections. The results showed no more disruption of elastic laminae than would be expected from simple physical displacement of elastic laminae. We conclude that if elastolysis contributes at all to invasion of vessel walls by aspergilli, then it seems to be very localized and/or transient.

Purification and characterization of a fibrinogenolytic serine proteinase from Aspergillus fumigatus culture filtrate

A fibrinogenolytic proteinase has been isolated from Aspergillus fumigatus culture filtrate by ammonium sulfate precipitation followed by successive chromatographies on Sephadex G-75 and immobilized phenylalanine. The purified proteinase exhibited a molecular weight of about 33 kDa. When analysed by SDS-polyacrylamide gels containing co-polymerized fibrinogen, the proteinase appeared as a broad band at the top of the gels, which could correspond to polymerization of the enzyme, as suggested by SDS-PAGE analysis of the unboiled eluate. The isoelectric point was 8.75 and the enzyme was not glycosylated. Proteinase activity was optimum at pH 9 and between 37 and 42 degrees C, although a decrease in activity was observed above 37 degrees C. PMSF and chymostatin markedly inhibited the proteinase activity, and good kinetic constants were obtained for the synthetic substrate, N-Suc-Ala-Ala-Pro-Phe-pNA. These results provide direct evidence that this enzyme belongs to the chymotrypsin-like serine proteinase group.

An Aspergillus fumigatus alkaline protease mutant constructed by gene disruption is deficient in extracellular elastase activity

Invasive pulmonary aspergillosis, usually caused by Aspergillus fumigatus, is a life-threatening condition of immunosuppressed patients. We have created a mutant strain of this fungus that lacks an extracellular alkaline protease (AFAlp). This was accomplished by transformation of A. fumigatus with a plasmid containing a selectable marker for hygromycin B resistance, and a 504 bp segment of the AFAlp gene, obtained by polymerase-chain-reaction-based amplification of A. fumigatus genomic DNA. Approximately 25% of transformants resulted from disruption of the AFAlp gene. SDS-polyacrylamide gel electrophoresis of proteins from the culture filtrate of a strain carrying the AFAlp gene disruption showed that it lacked a major protein of 33 kDa. Furthermore, in contrast to the culture filtrate from wild-type cells, the mutant had undetectable activity on azocollagen and elastin-Congo red, over a broad pH range. This shows that AFAlp accounts for most, if not all, of the extracellular elastinolytic activity of A. fumigatus, and that the mutant strain will be useful in assessing the role of AFAlp in pathogenicity.

Purification and properties of the elastase from Aspergillus fumigatus

Elastase, a potential virulence factor from the opportunistic pathogen Aspergillus fumigatus, was purified 220-fold from culture broth by fast-performance liquid chromatography employing anion exchange (Q Sepharose fast flow), cation exchange (S Sepharose fast flow), and gel filtration (Superose 12). Purified to near homogeneity, the elastase had an apparent molecular mass of 32 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (silver stain) but a mass of about 19.1 kDa as determined by gel filtration on Superdex 75. The elastase is not glycosylated and is positively charged at neutral pH, having a pI of 8.75. Inhibition by 0.2 mM phenylmethylsulfonyl fluoride (100%) and 0.21 mM leupeptin (60%) implies that the elastase is a serine protease. However, the enzyme is also inhibited by 5 mM EDTA (100%) and 10 mM 1,10-orthophenanthroline (30%), suggesting a requirement for divalent cations. The enzyme acts optimally at pH 7.4 and 45 degrees C in 50 mM sodium borate buffer, but in Tris HCl, the pH optimum shifts to 8.8.

Extracellular proteases of Aspergillus flavus. Fungal keratitis, proteases, and pathogenesis

To get a better understanding of the possible role of proteases in the pathogenesis of fungal keratitis, the extracellular proteases of a clinical isolate of Aspergillus flavus, from a severe case of keratitis, were identified and partially characterized. This strain, designated CU226/88, was grown with a variety of substrates as nitrogen sources, under conditions that would be expected to derepress the production of extracellular proteases. When grown on minimal medium with milk protein as a nitrogen source, the fungus appeared to produce primarily a metalloprotease, which has a zinc cofactor. When grown with insoluble collagen or elastin as a nitrogen source, a serine protease and cysteine protease, as well as the metalloprotease, are produced. Strain CU226/88 can grow with collagen, but not elastin, as the sole source of carbon as well as nitrogen. It is possible that the collagenase activity is a mediator of the severe corneal destruction caused by this isolate.

Isolation and characterization of an elastinolytic proteinase from Aspergillus flavus

An elastinolytic proteinase of Aspergillus flavus has been isolated to homogeneity, and its physical and biochemical properties have been characterized. Two purification protocols were compared; an initial step of ion-exchange chromatography was found to be equivalent to ammonium sulfate precipitation at neutral pH. A combination of gel filtration and adsorption chromatographies on the resultant crude enzyme produced highly purified elastase with yields of 5 to 10%. The enzyme is a 23-kilodalton protein with a pI of 7.6. The enzyme activity is markedly inhibited by numerous metal ions. Aspergillus elastase appears to be a metalloproteinase EC 3.4.24.X), as determined by its sensitivity to 1,10-phenanthroline.