P394 Evaluation of diagnostic potential of recombinant secretory aspartyl proteinase 2 (Sap2) protein from Candida parapsilosis for use in systemic candidiasis

POSTER SESSION 3, SEPTEMBER 23, 2022, 12:30 PM - 1:30 PM: OBJECTIVES: Systemic candidiasis is the fourth most common bloodstream infection in ICU patients worldwide. Along with Candida albicans, infections caused by non-albicans Candida (NAC) species are increasingly becoming more prevalent globally along with the emergence of drug resistance. The diagnosis of systemic candidiasis is difficult due to the absence of significant clinical symptoms in patients. Since conventional diagnostics methods for candidiasis show less sensitivity and specificity, novel immunodiagnostic techniques are needed for early diagnosis. We investigated the diagnostic potential of recombinant secreted aspartyl proteinase 2 (rSap2) from C. parapsilosis for the detection of Candida infection. METHODS: Genomic DNA was isolated from C. parapsilosis, followed by PCR amplification of Sap2 gene using designed gene-specific primers. Sap2 protein expression and purification was performed using Ni-NTA affinity chromatography under denaturing conditions. The denatured protein was subsequently refolded using a multi-step dialysis procedure. CD and FTIR studies were performed to confirm refolding. Mice were immunized with rSap2 protein and serum ELISA assays were performed for testing immunogenicity. Immunoblotting assays and human serum ELISAs were performed using whole-cell Candida and rSap2 protein in proven systemic candidiasis patient serum and controls, recruited at PGIMER, Chandigarh. RESULTS: Sap2 protein from C. parapsilosis was successfully cloned and expressed using an E. coli-based prokaryotic expression system. Protein refolding was performed in vitro using step-wise dialysis. Structural analysis by CD and FTIR spectroscopy revealed the refolded protein to be in its near native conformation. Immunogenicity analysis demonstrated the rSap2 protein to be highly immunogenic as evident from significantly high titers of Sap2-specific antibodies in antigen immunized BALb/c mice, compared to sham-immunized controls. The diagnostic potential of rSap2 protein was evaluated using immunoblotting and ELISA assays using serum from proven systemic candidiasis patients and controls. Our immunoblotting results demonstrate that the recombinant Sap2 protein was recognized as a single band of approximately 41 kDa by systemic candidiasis patient serum samples and no cross reactivity was observed in healthy controls. On evaluating the diagnostic potential of the rSap2 antigen using an ELISA-based approach, our results show that anti-Sap2 Ig, IgG and IgM antibodies could be detected in the sera of proven candidiasis patients. Of note, the differences in Sap2 antibody titers observed amongst patients and controls were similar to the serological response observed when heat-killed whole-cell Candida was used as a coating antigen. CONCLUSION: In summary, the rSap2 protein from C. parapsilosis has the potential to be used in the diagnosis of systemic candidiasis, providing a rapid, convenient, accurate, and cost-effective strategy. Our results indicate that the rSap2 protein from C. parapsilosis can be used to detect and diagnose systemic candidiasis infection in human patients and can be used as an alternative/replacement of whole-cell Candida-based ELISA procedures, which are currently in use.