Production of gliotoxin during the pathogenic state in turkey poults by Aspergillus fumigatus Fresenius

Virulence Factors Detection in Aspergillus Isolates from Clinical and Environmental Samples

INTRODUCTION

Pathogenesis of aspergillosis is dependent on various factors of the host (immune status) and virulence factors of the pathogen which could play a significant role in the pathogenesis of invasive aspergillosis.

AIM

To study the virulence factors of Aspergillus species isolated from patient samples and environmental samples.

MATERIALS AND METHODS

This prospective and experimental study was carried out at Department of Microbiology, MGM Medical College and Hospital, Mumbai, Maharashtra, India, from July 2014 to June 2015. For detection of virulence factors of Aspergillus species, total 750 samples were included in this study (350 from patients and 400 samples from environment). Patient samples and hospital environment samples were subjected to standard methods for screening of Biofilm, Lipase, α-amylase, proteinase, haemolysin, phospholipase and pectinase. Statistical analysis was done using Chi-square test and SPSS (Version 17.0).

RESULTS

American Type Culture Collection (ATCC) control of Aspergillus oryzae, Aspergillus niger and Aspergillus brasiliensis showed production of all virulence factors. In patient samples maximum virulence factor was produced i.e., α-amylase activity (89.74%) followed by proteinase activity (87.17%), biofilm production was (82.05%) haemolysin activity (79.48%), lipase activity (66.66%), pectinase activity and phospholipase activity (61.53%). In environment samples maximum virulence factor was produced i.e., proteinase activity (41.02%) followed by biofilm production was (38.46%), α-amylase activity (35.89%), haemolysin activity (33.33%), lipase activity (28.20%), phospholipase (25.64%) and pectinase activity (23.07%). The differences in patient and environment virulence factors were statistically significant (p-value <0.05).

CONCLUSION

Overall the presence of virulence factors was found more in Aspergillus species isolated from patient samples then environmental samples. This could be due to invasiveness nature of Aspergilli. Aspergillusniger was common isolates from both patient and environmental samples. Our study highlights the possible transmission of Aspergilli from environment to patient. Detection of virulence factors of Aspergillus species help to differentiate between pathogenic and non-pathogenic Aspergilli. Presence of virulence factors confirmed pathogenicity of the isolates. It also helps the physicians to treat the patient when appropriate treatment is needed.

Gliotoxin--bane or boon?

Gliotoxin (GT) is the most important epidithiodioxopiperazine (ETP)-type fungal toxin. GT was originally isolated from Trichoderma species as an antibiotic substance involved in biological control of plant pathogenic fungi. A few isolates of GT-producing Trichoderma virens are commercially marketed for biological control and widely used in agriculture. Furthermore, GT is long known as an immunosuppressive agent and also reported to have anti-tumour properties. However, recent publications suggest that GT is a virulence determinant of the human pathogen Aspergillus fumigatus. This compound is thus important on several counts - it has medicinal properties, is a pathogenicity determinant, is a potential diagnostic marker and is important in biological crop protection. The present article addresses this paradox and the ecological role of GT. We discuss the function of GT as defence molecule, the role in aspergillosis and suggest solutions for safe application of Trichoderma-based biofungicides.

Immunochemical analysis of fumigaclavine mycotoxins in respiratory tissues and in blood serum of birds with confirmed aspergillosis

The ergoline alkaloid fumigaclavine A (FuA) is one of the major mycotoxins produced by Aspergillus fumigatus, the main causative fungal agent of avian aspergillosis. To study in situ production of FuA, post-mortem respiratory tissues of various avian species, as well as blood samples of falcons (Falco sp.), were analysed by enzyme immunoassay (EIA). At a detection limit of 1.5 ng/ml, FuA EIA positive results were obtained for tissue samples from seven (64%) out of 11 birds with confirmed aspergillosis, with a maximum concentration of 38 ng/g, while all controls (n = 7) were negative. No FuA could be detected in blood serum (detection limit 0.7 ng/ml) of 15 falcons, experimentally inoculated with A. fumigatus conidia. Fungal mycelium material from tissue of clinical aspergillosis cases, cultured on malt extract agar, was highly positive in the FuA EIA in milligrams per gram range. Chromatographic analysis of mycelium extracts revealed the co-presence of FuA and the structurally related fumigaclavine C (FuC). Alkaline hydrolysis of FuA and FuC yielded the corresponding deacetylation products, FuB and FuE. This is the first report showing that fumigaclavine alkaloids are produced by A. fumigatus in situ during the course of clinical aspergillosis in birds; however, the role of these compounds in the pathogenesis of this disease is still unknown.

Aspergillus and aspergilloses in wild and domestic animals: a global health concern with parallels to human disease

The importance of aspergillosis in humans and various animal species has increased over the last decades. Aspergillus species are found worldwide in humans and in almost all domestic animals and birds as well as in many wild species, causing a wide range of diseases from localized infections to fatal disseminated diseases, as well as allergic responses to inhaled conidia. Some prevalent forms of animal aspergillosis are invasive fatal infections in sea fan corals, stonebrood mummification in honey bees, pulmonary and air sac infection in birds, mycotic abortion and mammary gland infections in cattle, guttural pouch mycoses in horses, sinonasal infections in dogs and cats, and invasive pulmonary and cerebral infections in marine mammals and nonhuman primates. This article represents a comprehensive overview of the most common infections reported by Aspergillus species and the corresponding diseases in various types of animals.

Antifungal and antihepatotoxic effects of sepia ink extract against oxidative stress as a risk factor of invasive pulmonary aspergillosis in neutropenic mice

BACKGROUND

There is a great need for novel strategies to overcome the high mortality associated with invasive pulmonary aspergillosis (IPA) in immunocompromised patients. To evaluate the antifungal and antihepatotoxic potentials of Sepia ink extract, its effect on liver oxidative stress levels was analyzed against IPA in neutropenic mice using amphotercin B as a reference drug.

MATERIALS AND METHODS

Eighty neutropenic infected mice were randomly assigned into four main groups. The 1(st) group was treated with saline, neutropenic infected (NI), the 2(nd) group was treated with ink extract (200 mg/kg) (IE) and the 3(rd) group was treated with amphotericin B (150 mg/kg) (AMB) and 4(th) group was treated with IE plus AMB. Treatment was started at 24 h after fungal inoculation (1×10(9) conidia/ml).

RESULTS

The present study revealed good in vitro and in vivo antifungal activity of IE against A. fumigatus. IE significantly reduced hepatic fungal burden and returns liver function and histology to normal levels. Compared with the untreated infected group, mice in the IE, AMB, and IE+ AMB groups had increased glutathione reduced (GSH) and superoxide dismutase (SOD) and significantly reduced malondialdehyde (MDA) levels at 24 and 72 h after inoculation with A. fumigatus conidia.

CONCLUSION

It is then concluded that in combination with antifungal therapy (AMB), IE treatment can reduce hepatic fungal burden, alleviate hepatic granulomatous lesions and oxidative stress associated with IPA in neutropenic mice.

Chronic illness associated with mold and mycotoxins: is naso-sinus fungal biofilm the culprit?

It has recently been demonstrated that patients who develop chronic illness after prior exposure to water damaged buildings (WDB) and mold have the presence of mycotoxins, which can be detected in the urine. We hypothesized that the mold may be harbored internally and continue to release and/or produce mycotoxins which contribute to ongoing chronic illness. The sinuses are the most likely candidate as a site for the internal mold and mycotoxin production. In this paper, we review the literature supporting this concept.

Fungal/mycotic diseases of poultry-diagnosis, treatment and control: a review

Fungal/mycotic diseases cause significant economic losses to the poultry industry either due to their direct infectious nature or due to production of mycotoxins, the secondary fungal metabolites produced in grains or poultry feed. Several fungi have created havoc in the poultry industry and some of them cause direct harm to human health due to their zoonotic implications. They are responsible for high morbidity and mortality, especially in young birds and cause stunted growth and diarrhea; and fatal encephalitis. Mycotic dermatitis is a possible health hazard associated with poultry houses. Mycotoxins are the leading cause of producing immunosuppression in birds, which makes them prone to several bacterial and viral infections leading to huge economic losses to the poultry industry. In comparison to bacterial and viral diseases, advances in diagnosis, treatment, prevention and control of fungal diseases in poultry has not taken much attention. Recently, molecular biological tools have been explored for rapid and accurate diagnosis of important fungal infections. Effective prevention and control measures include: appropriate hygiene, sanitation and disinfection, strict biosecurity programme and regular surveillance/monitoring of fungal infections as well as following judicious use of anti-fungal drugs. Precautionary measures during crop production, harvesting and storing and in feed mixing plants can help to check the fungal infections including health hazards of mycotoxins/mycotoxicosis. The present review describes the fungal pathogens causing diseases in poultry/birds, especially focusing to their diagnosis, prevention and control measures, which would help in formulating appropriate strategies to have a check and control on these unwanted troubles to the poultry producers/farmers.

Aspergillus fumigatus in Poultry

Aspergillus fumigatus remains a major respiratory pathogen in birds. In poultry, infection by A. fumigatus may induce significant economic losses particularly in turkey production. A. fumigatus develops and sporulates easily in poor quality bedding or contaminated feedstuffs in indoor farm environments. Inadequate ventilation and dusty conditions increase the risk of bird exposure to aerosolized spores. Acute cases are seen in young animals following inhalation of spores, causing high morbidity and mortality. The chronic form affects older birds and looks more sporadic. The respiratory tract is the primary site of A. fumigatus development leading to severe respiratory distress and associated granulomatous airsacculitis and pneumonia. Treatments for infected poultry are nonexistent; therefore, prevention is the only way to protect poultry. Development of avian models of aspergillosis may improve our understanding of its pathogenesis, which remains poorly understood.

The Aspergillus fumigatus toxin fumagillin suppresses the immune response of Galleria mellonella larvae by inhibiting the action of haemocytes

Larvae of Galleria mellonella are widely used to evaluate microbial virulence and to assess the in vivo efficacy of antimicrobial agents. The aim of this work was to examine the ability of an Aspergillus fumigatus toxin, fumagillin, to suppress the immune response of larvae. Administration of fumagillin to larvae increased their susceptibility to subsequent infection with A. fumigatus conidia (P = 0.0052). It was demonstrated that a dose of 2 µg fumagillin ml⁻¹ reduced the ability of insect immune cells (haemocytes) to kill opsonized cells of Candida albicans (P = 0.039) and to phagocytose A. fumigatus conidia (P = 0.016). Fumagillin reduced the oxygen uptake of haemocytes and decreased the translocation of a p47 protein which is homologous to p47(phox), a protein essential for the formation of a functional NADPH oxidase complex required for superoxide production. In addition, toxin-treated haemocytes showed reduced levels of degranulation as measured by the release of a protein showing reactivity to an anti-myeloperoxidase antibody (P<0.049) that was subsequently identified by liquid chromatography-MS analysis as prophenoloxidase. This work demonstrates that fumagillin suppresses the immune response of G. mellonella larvae by inhibiting the action of haemocytes and thus renders the larvae susceptible to infection. During growth of the fungus in the larvae, this toxin, along with others, may facilitate growth by suppressing the cellular immune response.

Aspergillus fumigatus toxicity and gliotoxin levels in feedstuff for domestic animals and pets in Argentina

AIMS

To evaluate gliotoxin production by Aspergillus fumigatus strains isolated from feedstuff intended for domestic animals and pets, and to determine the amount of gliotoxin in these substrates.

METHODS AND RESULTS

A total of 150 feedstuff samples were collected. They were composed of 30 samples each of five different feed types (pigs, poultry, cattle, horse and pets). Aspergillus fumigatus gliotoxin production ability and gliotoxin presence in feedstuff was determined by HPLC. Aspergillus fumigatus strains were isolated from all of the tested samples. Strains from cattle, horses and pet food were able to produce gliotoxin. Corn silage samples intended for cattle did not show gliotoxin contamination. All the other tested samples had gliotoxin levels ranging from 29 to 209 microg g(-1). Horse and poultry feed samples had the greatest contamination frequency.

CONCLUSIONS

Feed samples contaminated with gliotoxin are potentially toxic to animals.

SIGNIFICANCE AND IMPACT OF THE STUDY

The presence of gliotoxin could affect animal productivity and health. Moreover, there are risks of contamination to farm workers handling improperly stored animal feed. Aspergillus fumigatus strains isolated from different sources should be investigated to determine prevention and control strategies.

Translocation of proteins homologous to human neutrophil p47phox and p67phox to the cell membrane in activated hemocytes of Galleria mellonella

Activation of the superoxide forming respiratory burst oxidase of human neutrophils, crucial in host defence, requires the cytosolic proteins p47phox and p67phox which translocate to the plasma membrane upon cell stimulation and activate flavocytochrome b558, the redox centre of this enzyme system. We have previously demonstrated the presence of proteins (67 and 47kDa) in hemocytes of the insect Galleria mellonella homologous to proteins of the superoxide-forming NADPH oxidase complex of neutrophils. The work presented here illustrates for the first time translocation of homologous hemocyte proteins, 67 and 47kDa from the cytosol to the plasma membrane upon phorbol 12-myristate 13 acetate (PMA) activation. In hemocytes, gliotoxin (GT), the fungal secondary metabolite significantly suppressed PMA-induced superoxide generation in a concentration dependent manner and reduced translocation to basel nonstimulated levels. Primarily these results correlate translocation of hemocyte 47 and 67kDa proteins with PMA induced oxidase activity. Collectively results presented here, demonstrate further cellular and functional similarities between phagocytes of insects and mammals and further justify the use of insects in place of mammals for modelling the innate immune response to microbial pathogens.

Effect of N-chlorotaurine on Aspergillus, with particular reference to destruction of secreted gliotoxin

The fungistatic and fungicidal activity ofN-chlorotaurine (NCT), a long-lived oxidant produced by stimulated neutrophils, was investigated. Physiological concentrations (75–100 μM) of NCT showed clear fungicidal activity against a range ofAspergillusisolates. Moreover, killing by NCT was significantly increased in the presence of ammonium chloride, explained by the formation of monochloramine by halogenation of ammonium. One clinical isolate ofAspergillus fumigatuswas characterized for the production of the immunosuppressive agent gliotoxin, and NCT was shown to cause destruction of gliotoxin, possibly via reduction of the disulphide bridge. Because of its endogenous nature and its high antifungal activity, NCT appears to be a good choice for topical treatment ofAspergillusinfections, and the results of this study further substantiate its therapeutic efficacy.

Aspergillus mycotoxins and their effect on the host

Aspergillus fumigatus is known to produce various immunosuppressive mycotoxins including gliotoxin. However, none of these mycotoxins has been confirmed as being directly related to the pathogenesis of aspergilli. Recent studies have made substantial progress in the determination of mycotoxins as virulence factors. Gliotoxin was found to be produced much faster than previously believed under certain culture conditions, such as at 37 degrees C and under high oxygen content, which is close to the environment in the host. Gliotoxin was also found to be detectable in the sera of aspergillosis mice and of aspergillosis patients. Based on these findings, it is becoming evident that gliotoxin is produced in the infected organs of patients of aspergillosis at a significant level. In addition to these known mycotoxins, A. fumigatus produces many mycotoxins apparently different from known toxins. From the aspect of gene analysis, the deletion of laeA was found to block the expression of metabolic gene clusters such as sterigmatocystin, and the gene is also expected to be related to the production of gliotoxin. The significance of mycotoxins as virulence factors will hopefully be clarified in the near future.

Amphotericin B enhances the synthesis and release of the immunosuppressive agent gliotoxin from the pulmonary pathogen Aspergillus fumigatus

Exposure of the pulmonary pathogen Aspergillus fumigatus to amphotericin B alters membrane permeability as indicated by the escape of amino acids and protein from the mycelium. Amphotericin B exposure for periods of 2-4 h also leads to increased release of the immunosuppressive agent gliotoxin into the surrounding culture medium. Examination of the intracellular gliotoxin concentration following exposure to amphotericin B indicated elevated levels within the hyphae as well as in the culture medium--an effect which was also evident upon exposure of A. fumigatus to DMSO. These results indicate that in parallel with the ability of amphotericin B to act as a fungistatic agent it can also induce the synthesis of gliotoxin and facilitate its release by increasing the permeability of the fungal cell membrane. Increased synthesis of gliotoxin may result from the commencement of secondary metabolism in the presence of amphotericin B. The ability of amphotericin B to enhance the synthesis and release of gliotoxin may exacerbate the effects of the toxin and facilitate fungal invasion of pulmonary tissue.

Effects of Aspergillus fumigatus culture filtrate on antifungal activity of human phagocytes in vitro

BACKGROUND

Aspergillus fumigatus can colonise the airways and the lungs with localised underlying conditions and occasionally invade the surrounding lung tissues even in subjects without systemic predisposing factors, presumably by escaping the local host defences. The aim of this study was to investigate the effects of A fumigatus culture filtrate (ACF) on the activities of human phagocytes--inhibition of germination of A fumigatus spores by alveolar macrophages (AMs) and hyphal damage by polymorphonuclear leucocytes (PMNs)--which are the critical host defences against A fumigatus.

METHODS

Spores were incubated with AMs at a ratio of 1:1 in a medium containing different concentrations of ACF for 10 hours at 37 degrees C. Spore germination was visualised with light microscopy and the inhibition rate was calculated. The percentage of hyphal damage caused by PMNs pretreated with various concentrations of ACF was measured by a colorimetric tetrazolium metabolic assay.

RESULTS

The inhibition rate of spore germination by AMs cultured with medium alone (control) was 90 (0.8)% whereas that by AMs cultured with the medium containing 10% ACF was significantly (p < 0.05) reduced to 41.7 (4.6)%. ACF suppressed the inhibition of spore germination in a dose dependent manner without altering the phagocytosing activity against the spores. The percentage of hyphal damage caused by PMNs pretreated with medium-199 (control) was 78.1 (2.3)% compared with 65.3 (2.8)% when PMNs were pretreated with 50% ACF (p < 0.05).

CONCLUSIONS

A fumigatus releases biologically active substance(s) which suppress the inhibition of spore germination by AMs and also suppress PMN mediated hyphal damage, and thus may contribute to the pathogenicity of this fungus.

Natural occurrence of gliotoxin in turkeys infected with Aspergillus fumigatus, Fresenius

Thirteen samples of infected turkey lung tissue from cases of 'airsacculitis' were collected either at the processing plant or from a local turkey farm and subjected to cultural and gliotoxin analysis. Aspergillus fumigatus was isolated from 6 of the 13 samples; all isolates were determined to be gliotoxin producers when grown in laboratory culture and assayed by HPLC procedures. Gliotoxin was isolated from 5 of the 13 tissue but was not isolated from all tissues that were infected with A. fumigatus. Gliotoxin was isolated from which no A. fumigatus was isolated and it was not detected in three tissues from which gliotoxin-producing isolates of A. fumigatus were obtained. The ability of this pathogenic fungs to produce this immunomodulating compound in naturally infected turkeys provides further evidence that gliotoxin may be involved in the pathogenesis of the disease, aspergillosis of turkeys.