A Coconut-Agar Medium for Rapid Detection of Aflatoxin Production by Aspergillus spp.

Abstract

An agar medium containing commercial coconut extract and with pH adjusted to 6.9 was developed for detection of aflatoxin production by Aspergillus spp. On this medium, aflatoxin-positive, but not -negative, isolates showed a characteristic blue or blue-green fluorescence in agar surrounding the colonies when observed under UV light. The fluorescence produced by strong aflatoxin producers began to appear within 32 h after transfer to the medium. The intensity of fluorescence increased with prolonged incubation. An incubation time of 3 days was sufficient for detection of even very weak aflatoxin production. Several known aflatoxin promoters either had no effect or decreased the production of fluorescence. Incubation at 20.degree. C slightly reduced the intensity of fluorescence, whereas no difference was observed at 24, 28 or 32.degree. C. Seven of 27 Brazilian isolates of the A. flavus group that were tested on the medium were aflatoxin-positive; this was confirmed by TLC assay of culture broths. An orange-yellow pigmentation on the coconut-agar medium consistently was associated with the production of fluorescence and the aflatoxin-producing ability of Aspergillus spp. The pigmentation can be used to identify aflatoxin-positive isolates without the use of UV light. The medium is easy to prepare and aflatoxin detection is rapid and simple with only minimal equipment.