Antifungal activity of statins against Aspergillus species

Content Source – National Institutes for Health

The cholesterol-lowering agents known as statins have in vitro activities against human pathogenic fungi, such as Candida species, Cryptococcus neoformans, and Zygomycetes. Synergy between statins and azoles against these fungi has also been reported. We evaluated the in vitro activities of two statins, lovastatin and simvastatin, alone and in combination with azoles and amphotericin B, against clinical isolates of Aspergillus spp. A disk diffusion assay showed that both statins were active against Aspergillus spp. The minimal inhibitory concentration (MIC) ranges for lovastatin and simvastatin against Aspergillus spp. were 16 to >256 microg/ml and 4 to >256 microg/ml, respectively. Although both statins were fungicidal for A. fumigatus, the MICs were vastly higher than clinically achievable concentrations. The results of a combined agar dilution-Epsilometer test as well as a disk diffusion assay showed that neither statin had any effect on the in vitro activities of itraconazole, voriconazole, or amphotericin B against Aspergillus spp.

Blurred Lines-Pulmonary Aspergillosis and Lung Cancer

[18F]Fluorodexyglucose (FDG) positron emission tomography (PET) scans have significantly improved the diagnosis and staging of lung cancer, but false-positive scans are known to occur due to inflammatory and infectious diseases.

Recognition of the conditions leading to false-positive scans is important. Single or multiple pulmonary nodules, with or without cavitation, are classical findings in acute and chronic pulmonary aspergillosis. Clinical features of pulmonary aspergillosis are very similar to those of lung cancer.

This report highlights pulmonary aspergillosis as an alternative diagnosis to lung cancer in patients with positive [18F] FDG PET scans and the need to strive for presurgical histological diagnosis.

PDF: Pulmonary Aspergillus & Lung Cancer

Fungal Genome Initiative-Aspergillus Genome Projects

PROJECT BACKGROUND

Perhaps no other fungal genus contains species that are so harmful and species that are so beneficial to humans as the genus Aspergillus (1), and a large number of Aspergillus species are of biomedical and industrial significance. For example, A. nidulans is a key fungal model system for genetics and cell biology (2, 3), A. niger is widely exploited by the fermentation industry for the production of citric acid, whereas A. oryzae plays a key role in the fermentation process of several traditional Japanese beverages and sauces (4). In contrast, A. flavus is a plant and animal pathogen that also produces the potent carcinogen aflatoxin (5), whereas several other species (most notably A. fumigatus and A. terreus) are important opportunistic pathogens of individuals with compromised immune systems (6).

The genome sequences of A. nidulans (7), A. fumigatus (6) and A. oryzae (4) represented an enormous advance in the study of Aspergillus, providing the foundation for comparative and functional genomics studies. As part of the Fungal Genome Initiative, we have sequenced and annotated an additional Aspergillus species, A. terreus. Four additional recently sequenced genomes also fall within this phylogenetic group: A. flavusA. nigerA. clavatus, and Neosartorya fischeri. The profoundly different lifestyles exhibited by each of this growing set of Aspergillus species for which genome sequences are available coupled with the varying degrees of evolutionary affinity shared by their genomes make Aspergillus a model clade to address fundamental questions in functional and comparative genomics.

References

1. Volk, T., (1997) Aspergillus in Fungus of the Month, http://botit.botany.wisc.edu/toms_fungi/feb97.html
2. Pontecorvo, G., Roper, J. A., Hemmons, L. M., Macdonald, K. D. and Bufton, A. W. (1953) The genetics of Aspergillus nidulans. Adv. Genet. 5, 141-238.
3. Morris, N. R. and Enos, A. P. (1992) Mitotic gold in a mold: Aspergillus genetics and the biology of mitosis. Trends Genet. 8, 32-37.
4. Machida, M. et al. (2005) Genome sequencing and analysis of Aspergillus oryzae. Nature 438, 1157-1161.
5. Payne, G. A. et al. (2006) Whole genome comparison of Aspergillus flavus and A. oryzae. Med. Mycol. 44 Suppl, 9-11.
6. Nierman, W. C. et al. (2005) Genomic sequence of the pathogenic and allergenic filamentous fungus Aspergillus fumigatus. Nature 438, 1151-1156.
7. Galagan, J. E. et al. (2005) Sequencing of Aspergillus nidulans and comparative analysis with A. fumigatus and A. oryzae. Nature 438, 1105-1115.

Fungi and Human Pathogenesis

~ Content Source – Neal Chamberlain

Humans have a high level of innate immunity to fungi and most of the infections they cause are mild and self-limiting.

This resistance is due to:

  • 1. the fatty acid content of the skin.
  • 2. the pH of the skin, mucosal surfaces and body fluids.
  • 3. Epithelial cell turnover.
  • 4. Normal flora.
  • 5. Transferrin.
  • 6. Cilia of the respiratory tract.

When fungi do pass the resistance barriers of the human body and establish infections, the infections are classified according to the tissue levels initially colonized.

A. Superficial mycoses– infections limited to the outermost layers of the skin and hair.

B. Cutaneous mycoses– infections that extend deeper into the epidermis, as well as invasive hair and nail diseases.

These diseases are restricted to the keritinized layers of the skin, hair, and nails. Unlike the superficial mycoses, host immune responses may be evoked, resulting in pathologic changes expressed in the deeper layers of the skin. The organisms that cause these diseases are called dermatophytes. These diseases are often called ringworm or tinea. All the following diseases are causes by MicrosporumTrichophytonand Epidermophytonwhich comprise 41 species.

C. Subcutaneous mycoses- infections involve the dermis, subcutaneous tissues, muscle, and fascia. These infections are chronic and are initiated by trauma to the skin. These infections are difficult to treat and may require surgical intervention.

D. Systemic mycoses- infections that originate primarily in the lungs and may spread to many organ systems. These organisms are inherently virulent. All but Cryptococcus are dimorphic fungi.

Histoplasma capsulatum– Ohio and Mississippi river valleys, Yeast cells in tissue, Tuberculate macroconidia in mycelial phase.

Blastomyces dermatitidis– Ohio and Mississippi river valleys, Broad Base Budding yeast in tissue, Mycelia= microconidia

Coccidioides immitis– Southwestern US. Spherule in tissue, barrel-shaped Arthroconidia in mycelia phase.

Cryptococcus neoformans– Only yeast phase but unusual in that the cells are encapsulated as demonstrated by an India Ink stain.

E. Opportunistic mycoses– infections of patients with immune deficiencies who would otherwise not be infected. Ex. AIDS, altered normal flora, diabetes mellitus, immunosuppressive therapy, malignancy.

Candidiasis– Candida albicans– Creamy growth on various body surfaces. ex. mouth, skin, vagina. Budding yeast. Form pseudohyphae in tissue. Germ tube when grown in serum.

Aspergillosis– Aspergillus niger.

For more content download PDF Doc – Fungal Infections

Advances in citric acid fermentation by Aspergillus niger: Biochemical aspects, membrane transport and modeling

Research Review Paper

Maria Papagianni ⁎
Department of Hygiene and Technology of Food of Animal Origin, School of Veterinary Medicine, Aristotle University of Thessaloniki,
54006 Thessaloniki, Greece
Received 8 October 2006; received in revised form 11 January 2007; accepted 11 January 2007
Available online 19 January 2007

Content Source


Citric acid is regarded as a metabolite of energy metabolism, of which the concentration will rise to appreciable amounts only under conditions of substantive metabolic imbalances. Citric acid fermentation conditions were established during the 1930s and 1940s, when the effects of various medium components were evaluated.

The biochemical mechanism by which Aspergillus niger accumulates citric acid has continued to attract interest even though its commercial production by fermentation has been established for decades. Although extensive basic biochemical research has been carried out with A. niger, the understanding of the events relevant for citric acid accumulation is not completely understood. This review is focused on citric acid fermentation by A. niger.

Emphasis is given to aspects of fermentation biochemistry, membrane transport in A. niger and modeling of the production process.

© 2007 Elsevier Inc. All rights reserved.

PDF: Advances in citric acid fermentation by Aspergillus niger: Biochemical aspects, membrane transport and modeling

Additional reading-PDF: Comparative genomics of citric-acid-producing
Aspergillus niger ATCC 1015 versus enzyme-producing
CBS 513.88

Aspergillus Species

~ Content Source

Definition

• Aspergillosis is caused by species of the mold Aspergillus.

• Syndromes range from colonization; fungus ball due to Aspergillus (aspergilloma); allergic responses to Aspergillus, including allergic bronchopulmonary aspergillosis; to semi-invasive or invasive infections, from chronic necrotizing pneumonia to invasive pulmonary aspergillosis and other invasive syndromes.

Epidemiology

• The highest incidence of infection occurs in patients undergoing hematopoietic stem cell transplantation or solid-organ transplantation (see Table 259-2).

• Infection is more likely in patients with extensive immunosuppression or in those with relapse or recurrence of underlying malignancy.

• Improved survival has been noted with early diagnosis and newer therapies, but mortality rates in severely or persistently immunosuppressed patients are substantial.

Microbiology

• Culture-based diagnosis is useful to establish the specific diagnosis.

• Aspergillus species complexes exhibit distinct antifungal susceptibilities so that culture-based diagnosis is clinically relevant (see Table 259-1).

• Molecular analysis is required to establish species-level identity.

• Increasing rates of antifungal resistance are reported in some settings with a global clone of antifungal-resistant species.

Diagnosis

• Proven infection is established by culture of the organism.

• Biomarkers such as galactomannan, β-d-glucan, and polymerase chain reaction assay are useful for establishing probable diagnosis.

• Serial assessment of biomarkers may be useful for measuring response to therapy.

Therapy

• Voriconazole is recommended for primary therapy in most patients (see Table 259-4).

• Liposomal amphotericin B can be used as primary therapy in patients in whom voriconazole is not tolerated or contraindicated because of drug interactions or other reasons.

• Alternative agents for salvage therapy include amphotericin B lipid complex, the echinocandins (caspofungin, micafungin, or anidulafungin), posaconazole, or itraconazole.

• Combination therapy is not recommended for routine use, but some subgroups of patients (e.g., those with early diagnosis of infection based on detection of galactomannan or those with failure of primary therapy with a single agent) may benefit from such an approach.

Prevention

• Antifungal prophylaxis with posaconazole or possibly voriconazole is recommended in high-risk patients.

• The risk-benefit ratio of prophylaxis in individual patients at risk should be considered.

• Infection control is important to reduce risk in hospitalized patients, but long duration of risk (>180 days) in high-risk hematopoietic stem cell transplant or solid-organ transplant patients makes community-acquired infection likely.


Invasive aspergillosis is a major cause of morbidity and mortality in immunosuppressed patients. This infection is caused by Aspergillus, a mold with hyaline hyphae that is the etiologic agent in invasive aspergillosis and a variety of noninvasive or semi-invasive conditions. These syndromes range from colonization, such as fungus ball due to Aspergillus (also known as aspergilloma); allergic responses to Aspergillus, including allergic bronchopulmonary aspergillosis (ABPA); to semi-invasive or invasive infections, from chronic necrotizing pneumonia to invasive pulmonary aspergillosis and other invasive syndromes.

Aspergillus and the resultant aspergillosis are a major focus of clinical mycology because the number of patients with this disease has risen dramatically and because of the morbidity and mortality of this infection. The increased number of Aspergillus infections has occurred because more patients are at risk for this infection. Patients with established invasive aspergillosis have poor outcomes. Successful therapy depends not only on an early diagnosis but also on reversal of underlying immune defects. Even when therapy is begun promptly, outcomes are often poor, particularly in patients with disseminated or central nervous system disease and in those who remain profoundly immunosuppressed. New diagnostic approaches and new management strategies have been established. In this chapter, clinical mycology, epidemiology, pathogenesis, clinical presentation, diagnosis, treatment, and prevention of aspergillosis are described.


Mycology

The genus Aspergillus was first recognized in 1729 by Micheli, in Florence, who noted the resemblance between the sporulating head of an Aspergillus species and an aspergillum used to sprinkle holy water. In 1856, Virchow published the first complete microscopic descriptions of the organism. Aspergillus flavus was formally named by Link in 1809. Thom and Church first classified the genus in 1926 with 69 Aspergillus species in 11 groups. The term “group” is now more correctly referred to as “section,” but this reporting is not commonplace in clinical mycology laboratories. Because phenotypic methods and internal transcribed spacer sequencing identify Aspergillus isolates within a section and not individual species, it has been recommended that isolates should be reported as members of a “species complex.”

With the recent use of molecular techniques to characterize pathogenic fungi, aspergilli have now increased dramatically to include more than 250 species in eight subgenera (Aspergillus, Fumigati, Circumdati, Candidi, Terrei, Nidulante, Warcupi, and Ornati), which are subdivided into multiple sections and species complexes.

Most species of Aspergillus reproduce asexually, but a teleomorph (or sexual form with a fruiting body) has been identified for a number of species, including pathogenic species such as Aspergillus nidulans (teleomorph, Emericella nidulans), A. amstelodami (Eurotium amstelodami), A. udagawa (Neosartorya udagawae), and the most common pathogen A. fumigatus (Neosartorya fumigata) and many others. Even though the correct taxonomic nomenclature would rename these organisms using the sexual form, generally the generic name Aspergillus has been retained to simplify nomenclature regardless of their teleomorphs (sexual forms), rather than separating the organisms into unfamiliar species based on discovery of a sexual state. As with other pathogenic fungi, the taxonomy of Aspergillus has undergone extensive reclassification with utilization of molecular studies, such as sequencing of ribosomal, β-tubulin, calmodulin, or rodlet A genes, which has allowed more natural subgroupings of ascomycetous fungi. With identity established by means of molecular sequencing, the result of a familiar species may be reported as an unfamiliar telemorph, which has led to assigning one name to one fungus to clarify this potential confusion in clinical mycology.

The genus Aspergillus is an anamorphic member (asexual form) of the family Trichocomaceae. The teleomorphs (sexual forms) of Aspergillus species are classified in eight genera in the order Eurotiales in the phylum Ascomycota. Identification of the genus and of common pathogenic species is usually not difficult, but species-level identification of less common members can be laborious and misidentification of atypical or “cryptic” members of sections—such as poorly sporulating forms—is common.

The most common species causing invasive infection is Aspergillus fumigatus, the most common pathogen in the section Fumigati, which historically has made up a vast majority of invasive isolates: A. flavus; Aspergillus terreus; and, less commonly for invasive infection, Aspergillus niger. Recent studies have shown emergence of less common species, including A. terreus and unusual, less pathogenic species as the etiologic agents of invasive infection, including many “cryptic species” that are identifiable only by molecular studies. With more prolonged and profound immunosuppression—along with molecular identification of cryptic species within a species complex, the list of rare species causing invasive infection continues to increase, including A. alabamensis, A. alliaceus (teleomorph, Petromyces alliaceus), A. avenaceum, A. caesiellus, A. candidus, A. carneus, A. chevalieri (teleomorph, Eurotium chevalieri), A. clavatus, A. calidoustus, A. flavipes, A. fumigatiaffinis, A. glaucus, A. granulosus, A. insuetus, A. keveii, A. lentulus, A. nidulans (Emericella nidulans), A. novofumigatus, A. ochraceus, A. oryzae, A. puniceus, A. pseudodeflectus, A. restrictus, A. sydowii, Emericella quadrilineata (anamorph, A. tetrazonus), A. tamarii, A. tanneri, A. udagawa (Neosartorya udagawae), A. tubingensis, A. versicolor, A. viridinutans, A. vitus (teleomorph, Eurotium amstelodami), A. wentii, Neosartorya pseudofischeri, and many others, although the authenticity of at least some of these has been questioned and perhaps misidentified prior to molecular studies.

Pathogenic Aspergillus species are easily cultured from pathologic samples and grow rapidly (in 24 to 72 hours) on a variety of media. Blood cultures are uncommonly positive and usually reflect contamination rather than invasive disease. A distinguishing characteristic of pathogenic Aspergillus species is their ability to grow at 37° C. A. fumigatus is able to grow at 50° C, a feature that, in addition to morphology, can also be used to identify this species and can help distinguish A. fumigatus from cryptic Aspergillus species in the A. fumigatus complex. Most species initially appear as small, fluffy white colonies on culture plates within 48 hours. Presumptive identification of an Aspergillus species complex is usually accomplished by appearance of the fungus on gross and microscopic inspection of the colony, which provides typical sporulation, although specific species-level identification requires molecular confirmation so that laboratories should report isolates identified phenotypically as a “species complex.”

Microscopic features and colony morphology for the most common clinical isolates, A. fumigatus, A. flavus, A. terreus, and A. niger, are described in Table 259-1 and shown in Figures 259-1 to 259-4. Species-level identification of Aspergillus has become increasingly important because of differences in antifungal drug susceptibility.