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Published on: July 18, 2013
New Histoplasma Diagnostic Assays Designed via Whole Genome Comparisons
Juan E Gallo1,2,3, Isaura Torres1,3, Oscar M Gómez1,3
1Cellular and Molecular Biology Unit, Corporación para Investigaciones Biológicas (CIB), Medellín 05534, Colombia.
Abstract:
Histoplasmosis is a systemic fungal disease caused by the pathogen Histoplasma spp. that results in significant morbidity and mortality in persons with HIV/AIDS and can also affect immunocompetent individuals. Although some PCR and antigen-detection assays have been developed, conventional diagnosis has largely relied on culture, which can take weeks. Our aim was to provide a proof of principle for rationally designing and standardizing PCR assays based on Histoplasma-specific genomic sequences. Via automated comparisons of aligned genome contigs/scaffolds and gene (sub)sequences, we identified protein-coding genes that are present in existing sequences of Histoplasma strains but not in other genera. Two of the genes, PPK and CFP4, were used for designing primer sets for conventional and real-time PCR assays. Both resulted in a 100% analytical specificity in vitro and detected 62/62 H. capsulatum isolates using purified DNA. We also obtained positive detections of 2/2 confirmed H. capsulatum clinical FFPE (formalin-fixed paraffin-embedded) samples using both primer sets. Positive control plasmid 10-fold serial dilutions confirmed the analytical sensitivity of the assays. The findings suggest that these novel primer sets should allow for detection sensitivity and reduce false positive results/cross-reactions. New assays for detecting pathogenic fungi, constructed along these lines, could be simple and affordable to implement.
Insights
New PCR assays targeting Histoplasma DNA offer a faster and more accurate diagnosis for histoplasmosis. These novel primer sets demonstrate high specificity and sensitivity, potentially improving patient outcomes and reducing diagnostic delays.
Area of Science:
- Medical Mycology
- Molecular Diagnostics
- Infectious Diseases
Background:
- Histoplasmosis, a systemic fungal infection caused by Histoplasma spp., leads to significant illness and death, particularly in individuals with HIV/AIDS.
- Current diagnostic methods, primarily culture-based, are time-consuming, often taking weeks for results.
- Existing molecular assays lack standardization and comprehensive validation.
Purpose of the Study:
- To develop and validate novel PCR (polymerase chain reaction) assays for the rapid and accurate detection of Histoplasma.
- To identify and utilize unique Histoplasma genomic sequences for primer design.
- To establish a proof of principle for rationally designing standardized molecular diagnostic assays for fungal pathogens.
Main Methods:
- Bioinformatic analysis of aligned genome sequences to identify genus-specific genes.
- Design and synthesis of primer sets targeting the identified PPK and CFP4 genes.
- Development of conventional and real-time PCR assays.
- In vitro analytical specificity and sensitivity testing using purified DNA and clinical samples (FFPE).
Main Results:
- Two novel primer sets targeting PPK and CFP4 genes were successfully designed.
- Both primer sets exhibited 100% analytical specificity in vitro.
- The assays accurately detected all 62 tested Histoplasma capsulatum isolates and 2 clinical FFPE samples.
- Analytical sensitivity was confirmed through serial dilutions of control plasmids.
Conclusions:
- The developed primer sets enable sensitive and specific detection of Histoplasma, reducing the risk of false positives and cross-reactions.
- These novel assays represent a significant advancement over traditional culture methods, offering faster diagnosis.
- The rational design approach can be applied to develop affordable and simple molecular assays for other pathogenic fungi.
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