Real-time PCR based procedures for detection and quantification of Aspergillus carbonarius in wine grapes.

Aspergillus carbonarius is the main species responsible for ochratoxin A accumulation in wine grapes and consequently, its rapid and sensitive detection is increasingly investigated. A new real-time PCR (RTi-PCR) based procedure was developed for the rapid and specific detection and quantification of A. carbonarius in wine grapes. The procedure includes the use of the pulsifier equipment to remove conidia from grapes which prevents releasing of PCR inhibitors, and DNA extraction with the EZNA Fungal DNA kit. It reduced the time for A. carbonarius DNA extraction from grapes to 30 min. Two specific primers (AcKS10L/AcKS10R) delimiting a 161 bp fragment, and a probe were designed and directed to the beta-ketosynthase domain of a polyketide synthase from A. carbonarius. Specificity was confirmed by testing primers towards purified DNA from 52 fungal strains, including reference and food isolates. Quantification was linear over at least 5 log units using both serial dilutions of purified DNA and calibrated conidial suspensions from A. carbonarius. The SYBR-Green I and TaqMan RTi-PCR approaches established were able to detect at least 2.4 and 24 genomic equivalents, respectively, using purified DNA. Results obtained from conidial suspensions, after DNA extraction, showed that at least 5 conidia per reaction should be present for a positive result with SYBR-Green I and 50 in the case of TaqMan. The quantification of fungal genomic DNA in artificially inoculated wine grapes performed successfully, with a minimum threshold of 10(3) conidia mL(-1) for accurate quantification. The developed RTi-PCR assay is a promising tool in the prediction of potential ochratoxigenic risk, even in the case of low-level infections, and suitable for a rapid, automated and high throughput analysis.