Detection of Aspergillus DNA by a nested PCR assay is superior to blood culture in an experimental murine model of invasive aspergillosis

Development of a murine model to study the cerebral pathogenesis of Aspergillus fumigatus

IMPORTANCE

Molds are environmental fungi that can cause disease in immunocompromised individuals. The most common pathogenic mold is Aspergillus fumigatus, which is typically inhaled into the lungs and causes invasive pulmonary disease. In a subset of these patients, this infection can spread from the lungs to other organs including the brain, resulting in cerebral aspergillosis. How A. fumigatus causes brain disease is not well understood and these infections are associated with extremely high mortality rates. Thus, we developed an animal model to study the pathogenesis of cerebral aspergillosis to better understand this disease and develop better treatments for these life-threatening infections.

Rare Fungal Infection Linked to a Case of Juvenile Arthritis

Juvenile arthritis with unknown disease etiology is also known as juvenile idiopathic arthritis. Symptoms include joint pain, swelling, and stiffness, and standard treatment involves immunosuppressant medication. Here we present a case of juvenile idiopathic arthritis with severe malnutrition and worsening of symptoms, which restrained a nine-year-old girl to a wheelchair with minimal movement capacity and low energy during standard immunosuppressant therapies over the course of three years. Our innovative Pathogen Blood Test combining cytology-based microscopy and genetic analysis using a pan-fungal primer assay and sequencing identified a systemic fungal infection with Sagenomella species, closely related to Aspergillus, and a soil-dwelling highly pathogenic fungus, which had previously been linked to a fatal veterinary case of arthritis and malnutrition. Our test results encouraged a radical change of the patient's treatment plan, including cessation of the regular immunosuppressants, including steroids, over six months. The patient made a progressive recovery, including complete reversion of the previously swollen and painful joints, development of a good appetite, and return to liveliness. Within the year of change from immunosuppressants to immune-supportive integrative nutritional therapies, including regular intravenous vitamin C, and oral vitamin D, as well as gentle aqua- and physiotherapy, the patient started to gain weight including muscle mass and regained strength and movement in the hands, arms, and legs. She was able to walk again within 18 months. Her mood and energy levels continued to improve and she was able to return to school full-time.

Rodent Models of Invasive Aspergillosis due to Aspergillus fumigatus: Still a Long Path toward Standardization

Invasive aspergillosis has been studied in laboratory by the means of plethora of distinct animal models. They were developed to address pathophysiology, therapy, diagnosis, or miscellaneous other concerns associated. However, there are great discrepancies regarding all the experimental variables of animal models, and a thorough focus on them is needed. This systematic review completed a comprehensive bibliographic analysis specifically-based on the technical features of rodent models infected with Aspergillus fumigatus. Out the 800 articles reviewed, it was shown that mice remained the preferred model (85.8% of the referenced reports), above rats (10.8%), and guinea pigs (3.8%). Three quarters of the models involved immunocompromised status, mainly by steroids (44.4%) and/or alkylating drugs (42.9%), but only 27.7% were reported to receive antibiotic prophylaxis to prevent from bacterial infection. Injection of spores (30.0%) and inhalation/deposition into respiratory airways (66.9%) were the most used routes for experimental inoculation. Overall, more than 230 distinct A. fumigatus strains were used in models. Of all the published studies, 18.4% did not mention usage of any diagnostic tool, like histopathology or mycological culture, to control correct implementation of the disease and to measure outcome. In light of these findings, a consensus discussion should be engaged to establish a minimum standardization, although this may not be consistently suitable for addressing all the specific aspects of invasive aspergillosis.

The aspHS gene as a new target for detecting Aspergillus fumigatus during infections by quantitative real-time PCR

Invasive aspergillosis (IA) is a serious nosocomial infection caused by Aspergillus spp. which has a high mortality rate due to the fact, among other factors, that it is difficult to diagnose. Within the Aspergillus genus, A. fumigatus is the main species causing IA. We propose a virulence factor, the aspHS gene, as a novel target for the specific detection of A. fumigatus by quantitative real-time PCR (qPCR). This target gene encodes a haemolysin, which is overexpressed in vivo during infection. We have designed specific primers and hydrolysis (Taqman) probes for the detection of this target and a chimeric internal amplification control (IC), designed to detect false negative results due to PCR inhibition. This qPCR assay was tested with DNA extracted from a wide collection of microorganisms, tissues from infected mice, and human bronchoalveolar lavage (BAL) samples. Results showed that it, together with the DNA extraction method, could detect A. fumigatus with high specificity. Furthermore, it can distinguish between germinated (first step to the development of infection) and non-germinated conidia (not detected). Our data indicate that these techniques could be sufficiently sensitive and rapid to help clinicians establish an earlier diagnosis, but the presence of PCR inhibitors in clinical samples such as BAL fluids needs to be addressed.

Detection of Aspergillus DNA by a nested PCR assay is able to improve the diagnosis of invasive aspergillosis in paediatric patients

Fungal infections are a leading cause of morbidity and mortality in severely immunocompromised patients and have been increasing in incidence in recent years. Invasive aspergillosis (IA) is the most common filamentous fungal infection and is, in adults as well as in children, difficult to diagnose. Several PCR assays to detect Aspergillus DNA have been established, but so far, studies on molecular tools for the diagnosis of IA in children are few. We evaluated the results of a nested PCR assay to detect Aspergillus DNA in clinical samples from paediatric and adolescent patients with suspected IA. Blood and non-blood samples from immunocompromised paediatric and adolescent patients with suspected invasive fungal infection were sent for processing Aspergillus PCR to our laboratory. PCR results from consecutive patients from three university children's hospitals investigated between November 2000 and January 2007 were evaluated. Fungal infections were classified according to the EORTC classification on the grounds of clinical findings, microbiology and radio-imaging results. Two hundred and ninety-one samples from 71 patients were investigated for the presence of Aspergillus DNA by our previously described nested PCR assay. Two, 3 and 34 patients had proven, probable and possible IA, respectively. Sensitivity (calculated from proven and probable patients, n=5) and specificity (calculated from patients without IA, n=32) rates of the PCR assay were 80 and 81 %, respectively. Our nested PCR assay was able to detect Aspergillus DNA in blood, cerebrospinal fluid and bronchoalveolar lavage samples from paediatric and adolescent patients with IA with high sensitivity and specificity rates.

Diagnostic value of DNA, (1-3)-β-d-glucan, and galactomannan detection in serum and bronchoalveolar lavage of mice experimentally infected with Aspergillus terreus

The aim of this study was to evaluate the diagnostic value of Aspergillus terreus-specific DNA, (1-3)-beta-d-glucan (BDG), and galactomannan (GM) in immunosuppressed mice infected intravenously with A. terreus conidia and sacrificed in groups of 12 each on days 1, 3, 5, 7, and 9. A. terreus-specific DNA, BDG, and GM in serum and bronchoalveolar lavage (BAL) were detected by nested polymerase chain reaction (nPCR), Fungitell kit (Associates of Cape Cod, E. Falmouth, MA), and Aspergillus Platelia kit (Bio-Rad, Marnes-laCoquette, France), respectively. Cultures of lung homogenate of all the animals yielded A. terreus. The BDG positivity, GM positivity, and nPCR positivity in serum specimens were 43%, 78%, and 73%, respectively. Combined detection enhanced the positivity to 95% for A. terreus DNA and GM, 83% for GM and BDG, and 95% for DNA, GM, and BDG. In BAL, the GM positivity and nPCR positivity were 80% and 81%, respectively, whereas combined detection increased the positivity to 98%. Detection of GM and DNA offers a sensitive and specific diagnostic option for invasive aspergillosis.

Detection of Aspergillus DNA in cerebrospinal fluid from patients with cerebral aspergillosis by a nested PCR assay

Invasive aspergillosis (IA), a complication with high mortality rates, especially in disseminated IA with cerebral involvement, is difficult to diagnose. Biopsy of cerebral lesions is often not feasible, and culture of Aspergillus spp. from cerebrospinal fluid (CSF) is frequently negative. New molecular methods have emerged for diagnosing IA. So far, there are only few reports of Aspergillus DNA detection in CSF. After modifying the DNA extraction protocol, we detected Aspergillus DNA in CSF samples by a previously described nested PCR assay. In six patients with hematologic malignancy and cerebral aspergillosis, CSF samples were investigated for Aspergillus DNA. IA was classified according to the EORTC/MSG 2002 criteria. Two patients each had proven, probable, and possible IA. Thirty-five CSF samples were investigated for Aspergillus DNA by nested PCR. Samples with positive results in the nested PCR assay were quantified by LightCycler PCR assay. Fourteen CSF samples showed positive results in the nested PCR assay. Of these, six samples gave positive results in real-time PCR. The range of CFU per ml was 2,154 to 63,100,000. The highest number of CFU per ml was found in a CSF sample of a patient with acute lymphocytic leukemia and probable cerebral aspergillosis. Detection of Aspergillus DNA in CSF samples is thus possible and has the potential to improve diagnosis of cerebral aspergillosis. Further prospective studies with larger numbers of patients must be performed to evaluate the clinical significance of Aspergillus PCR with CSF samples.

Detection of fungal DNA by real-time polymerase chain reaction: evaluation of 2 methodologies in experimental pulmonary aspergillosis

The capabilities of 2 quantitative polymerase chain reaction (PCR) assays for detecting pulmonary aspergillosis were analyzed. Both methodologies were real-time (RT) based and were compared with quantitative cultures and galactomannan (GM) antigen detection in a rabbit model of invasive aspergillosis. A total of 106 samples including blood, serum, lung, and brain from 3 controls and 9 infected New Zealand rabbits were analyzed. The RT-PCR methodologies were an Aspergillus fumigatus-specific assay using fluorescent resonance energy transfer technology targeting a highly conserved region of the fungal 18S rRNA gene and a panfungal assay to amplify the internal transcribed spacer regions 1 and 2 from fungal rRNA gene complex, employing SYBRGreen fluorescent dye as a detector. The specificity for both PCR base assays, culture, and GM determination was 100%. The sensitivity of the specific PCR assay was 88.9% in lung samples, 66.6% in serum, 55.5% in blood, and 33.3 in brain specimens. The panfungal assay had a sensitivity of 33.3% in lung and serum samples, being brain and blood specimens invariably negative. Otherwise, 100% of the lungs resulted positive for culture, and all serum samples showed a GM index above 1.0 after 2 days of infection. The specific RT-PCR assay is a reliable technique to detect A. fumigatus DNA in vivo comparable to cultures and GM determination. The panfungal RT-PCR assay exhibited low sensitivity to diagnose invasive aspergillosis in rabbits advising against its clinical introduction.

Comparison of three methodologies for the determination of pulmonary fungal burden in experimental murine aspergillosis

Quantitative culture, quantitative PCR and the galactomannan enzyme immunoassay (EIA) were compared for their ability to determine the pulmonary fungal burden in a murine model of invasive aspergillosis. Quantitative culture of specimens containing hyphae under-represented the absolute fungal burden in established infection when compared with the two other methods. The best correlation was observed between the two non-culture methods. Higher variability was observed with the galactomannan EIA when compared with quantitative PCR. Collectively, these data suggest that quantitative PCR is the preferred method for determination of the pulmonary fungal burden in experimental aspergillosis.

The evolution and evaluation of a whole blood polymerase chain reaction assay for the detection of invasive aspergillosis in hematology patients in a routine clinical setting

BACKGROUND

Invasive aspergillosis (IA) is associated with high mortality. Successful outcome with treatment is linked to early diagnosis. The utility of classic diagnostic methods, however, is limited.

METHODS

To aid in the diagnosis of IA, we retrospectively assessed our diagnostic service, using real-time polymerase chain reaction (PCR) and galactomannan sandwich enzyme-linked immunosorbent assay (ELISA).

RESULTS

A total of 203 patients at risk of invasive fungal infection were screened by PCR, and 116 of the patients were also tested by ELISA. The patient group comprised 176 patients with hematological malignancy and 28 control patients with evidence of invasive candidal infection. Consensus European Organisation for Research and Treatment of Cancer and Mycoses Study Group criteria were used to classify fungal infection, which, by definition, excluded the PCR result. The PCR method was sensitive (up to 92.3% sensitivity) and specific (up to 94.6% specificity) and had good agreement with the galactomannan ELISA (76.7%) and high-resolution computed tomography scan results.

CONCLUSIONS

A negative PCR result can be used to rule out IA and to limit the need for empirical antifungal therapy; thus, it has a role in diagnosing IA infections, especially in combination with antigen testing. PCR-positive cases classified as "false positives" regularly reflect the limitations of classic microbiological procedures or restricted use of consensus clinical methods employed to classify infection.

Aspergilluspolymerase chain reaction (PCR) diagnosis

In recent years novel molecular methods, notably polymerase chain reaction (PCR) assays, have been developed to improve the diagnosis of life-threatening invasive aspergillosis in patients at high risk, especially patients with malignant hematological disease. Early diagnosis and treatment are essential for adequate therapeutic management. Management, however, often remains difficult since most of the diagnostic tools used clinically at present either lack specificity or acceptable sensitivity. The clinical value, advantages and remaining problems of PCR approaches to detect the emerging fungal pathogen are reviewed.