P407 Standardization of PCR for the diagnosis of invasive aspergillosis and invasive mucormycosis from blood samples
Authors: Rompally Satwika , Choudary Hansraj , Rudramurthy Shivaprakash M , Kaur Harsimran , Bansal Deepak , Malhotra Pankaj , Narayana Yaddanapudi Lakshmi , Chakrabarti Arunaloke 
Published: September 2022

Abstract

Poster session 3, September 23, 2022, 12:30 PM - 1:30 PM

Objectives
(1) Standardization of PCR-based diagnosis of invasive aspergillosis and invasive mucormycosis in spiked blood samples. (2) Standardization of PCR-based diagnosis of invasive aspergillosis and invasive mucormycosis in proven cases. (3) Validation of the above-standardized protocol in patients with proven/probable invasive aspergillosis or mucormycosis.

Materials and Methods
Blood samples were collected from healthy volunteers and patients with proven mucormycosis, proven invasive aspergillosis, and suspected invasive fungal infection. Standard strains of Mucorales and Aspergillus spp. were collected from the National Culture Collection of Pathogenic Fungi, PGIMER and DNA was extracted using a modified protocol of the fungal DNA extraction method by Lee and Taylor (1990). Mucor-specific primer (ZM13), described by Bialek R et al. (2005) was used for mucormycosis samples. Aspergillus specific primer pair was designed from mitochondrial DNA of A. fumigatus using Primer3 software. Genomic DNA was used to determine the optimum annealing temperature and concentration for ZM13 assay. DNA extracted from whole blood samples of healthy volunteers after spiking with a known quantity of A. fumigatus DNA and only genomic DNA was used separately to optimize annealing temperature and concentration of Aspergillus-specific primers. Similarly, whole blood, plasma, and serum samples from healthy volunteers were spiked with various concentrations of Rhizopus arrhizus and A. fumigatus DNA. DNA extracted from spiked samples was used to determine the analytical sensitivity of PCR assays. DNA extracted from blood samples of ten proven mucormycosis and five invasive aspergillosis patients were used to determine the optimum sample dilution factor and template volume for the assay. The final standardized protocols were validated using 28 proven/probable cases of invasive aspergillosis and invasive mucormycosis and thirty cases of suspected invasive fungal infection.

Results
The optimum annealing temperature and primer concentrations for the assay were 54.3°C and 0.4μm respectively for ZM13 assay and 53°C and 0.45μm respectively for Aspergillus assay. The limit of detection was 0.06fg/μl for ZM13 assay and 0.08fg/μL for Aspergillus specific assay. For mucormycosis assay, the slope of the standard curve was −3.2687 and the percentage efficiency of the assay was 104% with 0.9936 as the coefficient of determination (R2). Likewise, the slope of the standard curve was −3.2695, the percentage efficiency of the assay 102%, and the coefficient of determination (R2) 0.9858 for aspergillosis assay. The best combination of template volume and sample dilution factor was 2.5 μl and 1000x in whole blood samples and, 2.5 μl and 100x in serum samples for mucormycosis assay. It was 1.0 μl and 10x in serum samples for Aspergillus specific assay. The sensitivity, specificity, positive predictive value, and negative predictive value of mucormycosis qPCR using serum samples were 79.3%, 86.4%, 65.7%, and 92.7% respectively. The assay had a positive likelihood ratio of 5.92 and a negative likelihood ratio of 0.24.

Conclusion
The real-time PCR protocols standardized for the diagnosis of mucormycosis and invasive aspergillosis from blood samples showed promising results. However, the assay needs further validation in a larger study population.