A PCR method to identify ochratoxin A-producing Aspergillus westerdijkiae strains on dried and aged food

Authors: SUSCA, ANTONIA - National Research Council - Italy; ANELLI, PAMELA - National Research Council - Italy; HAIDUKOWSKI, MIRIAM - National Research Council - Italy; EPIFANI, FILOMENA - National Research Council - Italy; Probyn, Crystal; MORETTI, ANTONIO - National Research Council - Italy; LOGRIECO, ANTONIO - National Research Council - Italy; Proctor, Robert

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2021
Publication Date: 4/16/2021
Citation: Susca, A., Anelli, P., Haidukowski, M., Probyn, C.E., Epifani, F., Logrieco, A.F., Moretti, A., Proctor, R.H. 2021. A PCR method to identify ochratoxin A-producing Aspergillus westerdijkiae strains on dried and aged food. International Journal of Food Microbiology. 344. Article 109113. https://doi.org/10.1016/j.ijfoodmicro.2021.109113.
DOI: https://doi.org/10.1016/j.ijfoodmicro.2021.109113

Interpretive Summary: Ochratoxins are a group of fungal toxins that pose health risks to humans because of their toxicity and their frequent occurrence in diverse foods, including raisins, cereals, coffee, spices, cured meat, and cheese. The fungus Aspergillus westerdijkiae produces ochratoxins and is frequently isolated from the surface of traditional cheese varieties that are aged in caves in Europe and that can contain high levels of ochratoxins. In the current study, we analyzed strains of A. westerdijkiae isolated from cave-aged cheese and found that strains of the fungus that do not produce ochratoxin lack one of the five genes that are required by the fungus to synthesis the toxins. We used this information to develop a DNA-based test that can rapidly detect ochratoxin-producing strains of A. westerdijkiae that occur in cheese and other food products. The most effective way to prevent human consumption of ochratoxin-contaminated cheese and meat is to determine whether these foods contain the toxins or toxin-producing fungi, and then remove contaminated products from the supply chain. The DNA-based test will enhance food safety by rapidly detecting ochratoxin contaminated food.

Technical Abstract: Ochratoxins are a group of mycotoxins that frequently occur as contaminants in a variety of agricultural commodities and foods, including dry-cured meats and cheese. The fungus Aspergillus westerdijkiae is frequently isolated from aged food and can produce ochratoxin A (OTA). However, there is evidence that some A. westerdijkiae strains do not produce OTA. Monitoring and early detection of growth of OTA-producing fungi in food are the most effective strategies to manage OTA contamination. Therefore, we examined genome sequence data from four strains A. westerdijkiae isolated from the surface of cheese produced in southern Italy to identify genetic markers for OTA production. This analysis revealed a naturally occurring deletion of the OTA regulatory gene, otaR, in an OTA-nonproducing isolate of the fungus. We used this information to design a PCR-based A. westerdijkiae detection method. The method includes PCR primers complementary to conserved sequences located upstream and downstream of the otaR coding region. The primers yield different-sized amplicons in assays with OTA-producing versus nonproducing isolates of A. westerdijkiae, but they do not yield ota-region-specific amplicons from other OTA-producing fungi. Therefore, method is both specific to A. westerdijkiae but can also distinguish between the genetic potential of strains to produce OTA. Such an assay has a significant potential to improve OTA detection and monitoring programs.