Improvement of the Culture Medium for the Dichlorvos-Ammonia (DV-AM) Method to Selectively Detect Aflatoxigenic Fungi in Soil

Abstract

The dichlorvos-ammonia (DV-AM) method is a simple but sensitive visual method for detecting aflatoxigenic fungi. Here we sought to develop a selective medium that is appropriate for the growth of aflatoxigenic fungi among soil mycoflora. We examined the effects of different concentrations of carbon sources (sucrose and glucose) and detergents (deoxycholate (DOC), Triton X-100, and Tween 80) on microorganisms in soils, using agar medium supplemented with chloramphenicol. The results demonstrated that 5–10% sucrose concentrations and 0.1–0.15% DOC concentrations were appropriate for the selective detection of aflatoxigenic fungi in soil. We also identified the optimal constituents of the medium on which the normal rapid growth of Rhizopus sp. was completely inhibited. By using the new medium along with the DV-AM method, we succeeded in the isolation of aflatoxigenic fungi from non-agricultural fields in Fukui city, Japan. The fungi were identified as Aspergillus nomius based on their calmodulin gene sequences. These results indicate that the new medium will be useful in practice for the detection of aflatoxigenic fungi in soil samples including those from non-agricultural environments.

Detection of aflatoxigenic fungi in imported raw nuts using the dichlorvos-ammonia (DV-AM) method

“…The DV-AM method routinely uses YES-DOC-CP-DV agar medium 7) . After 15 ml of YES-DOC-CP agar medium (2% yeast extract, 10% sucrose, 0.1% Na DOC [Fujifilm Wako Pure Chemical Co., Osaka, Japan], 0.1 g chloramphenicol [CP]/L, and 2% agar) was poured and solidified in a plastic petri, 20 µl of 100-fold diluted DV (Wako, Osaka, Japan) methanol solution was spread onto the surface of the resulting medium.…”

“…Aflatoxigenic fungi may be widely distributed around the world. There have been no reports of crops grown on the mainland of Japan that are heavily contaminated with AFs, whereas aflatoxigenic fungi have been detected in the Kanto and the Hokuriku areas, which are the central parts of Japan's mainland 6), 7) . The origin and dynamic distribution of the aflatoxigenic fungi in Japan is thus important to prevent future possible contaminations of AFs in crops in Japan.…”

Chemical remediation of Aflatoxin B1 using encapsulated polyvinylpyrrolidone as an environmental-friendly control.

“…β-glucans is also involved in both hydrogen and Van der Waals bonding with AFB 1 although (1,6)-β-glucan is involved in only Van der Waals bonding. The (1,3)-β-D-glucan chains form triple helix three-dimensional structures with springlike mechanical properties and are responsible for the strength of yeast cell walls (1,3) and their ability to bind toxins [48,49]. Taken together, the ability of PVP-TA NPs and glucans to bind AFB 1 suggested that these agents strongly bind AFB 1 and decrease its bioavailability in the gastrointestinal tract and consequently reduce its toxicity.…”

“…They are produced mainly by certain strains of Aspergillus flavus and Aspergillus parasiticus, as well as several other species such as A. nomius [2], and more. The contamination of agricultural commodities with AFs is not only a serious health hazard to humans and animals, but also a cause of huge economic losses worldwide [3].…”

Occurrence Evaluation of Aflatoxigenic <i>Aspergilli</i> in Thai Corn Using Dichlorvos-ammonia and Whole-agar Extraction Methods

“…Based on these results, the objectives of this study were: 1) to apply the recently developed DV-AM and whole-agar extraction methods to detect aflatoxigenic fungi on corn grains; 2) to compare the occurrence of aflatoxigenic fungi among areas and grades in Thailand; and 3) to analyze the relationship between the emergence of aflatoxigenic fungal colonies and AFs' contamination level on grains. In the first experiment, corn grain samples were randomly collected from the northern and central parts of Thailand and analyzed for the presence of aflatoxigenic fungi using the improved DV-AM method with DV-coated yeast extract-sucrose-deoxycholate-chloramphenicol (YES-DOC-CP) agar (Yabe et al 2018). Owing to difficulties involved in DV usage in Japan, the second experiment included the whole-agar extraction method to assess the occurrence of aflatoxigenic fungi using DV-free YES-DOC-CP agar (Kishimoto et al 2023).…”