Establishment of fast diagnostic assays of Candida spp. in blood samples based on M1 beads enrichment

  Objective  To establish three fast assays (real-time PCR, micro-culture and plate cultures assays) based on recombined mannose-binding lectin (MBL) protein-magnetic beads enrichment technique for the detection of Candida spp. directly from whole blood.

  Methods  Three lysates (yeast lysate, LSTE and TXTE) were compared to determine the efficiency of Candida DNA extraction according to the amplification effects of real-time PCR. Five kinds of micro-culture medium (PBS, SA, YPD, LB and BHI) were compared for Candida culture efficiency by calculating the amount of Candida after culture. The efficiencies of three new assays for the Candida DNA extraction were evaluated using human plasma simulated samples and compared with standard blood cultures.

  Results  Compared with TXTE and LSTE, yeast lysate had the best DNA extraction effect for trace amount of Candida. The amount of Candida in SA, YPD, LB and BHI micro-culture media increased with time, especially for BHI. In the human plasma simulated samples, real-time PCR assay could detect Candida in the shortest time (3.75 h), but it could not detect all positive samples. Compared with standard blood culture assay, the identification results of micro-culture and plate-culture were obtained at least 39 h and 22 h earlier, respectively, and the sensitivity could reach 10 CFU/mL.

  Conclusion  Compared with standard blood culture assay, the real-time PCR, micro-culture and plate culture assays need much less time and have high specificity and sensitivity.