Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2017

Improved screening for aflatoxin producing fungi using almond agar fluorescence versus coconut containing agars (#224)

Cameron L Jones 1
  1. Biological Health Services, TOORAK, VIC, Australia

The Genus Aspergillus impacts human and animal health through direct infections as well as from production of virulence factors or mycotoxins like gliotoxin, ochratoxin, citrinin and sterigmatocystin1A. flavus and A. parasiticus are two species that produce aflatoxins, which are secondary metabolite, polyketide compounds that are carcinogenic, teratogenic, immunosuppressive and mutagenic.  There are four main aflatoxins: B1, B2, G1 and G2. Up to 25% of crops are thought to be contaminated with mycotoxins, with aflatoxin B1 being the major toxin.  Liver and gall-bladder cancers are strongly correlated with aflatoxin ingestion and exposure2.  There is a need for culture methods that can identify aflatoxin-producing fungi sampled from surfaces or from the air in order to assess contamination risk and environmental exposure. Fungi that secrete aflatoxins in agar containing coconut cream or coconut milk are known to fluoresce blue-green-yellow (BGY) under 365nm UV light. This paper presents an extension to this fluorescent screening tool for the identification of aflatoxin producing (toxigenic) fungi using almond milk as an alternative to coconut containing agars3-4. Coconut agars solidify with an oily, uneven surface, not well suited to streak inocula, while almond milk agar is smooth. Different agar media were prepared with Oxoid Agar No. 1 using coconut cream (CCA), coconut milk (CMA), almond milk, full-strength (AMNA) and almond milk, half-strength (AMA). Five reference A. flavus spp. and five A. parasiticus spp. producing combinations of: B1, B2, G1, G2, M1, M2 and no aflatoxin were screened. Fluorescence production was recorded daily from the reverse plate side. The characteristic BGY fluorescence started for some spp. in some of the coconut agars after 24hrs.  But over time and by day 3 the yellow colour dominated, matching the mycelial growth front, and no other fluorescence could be seen.  In contrast, the almond milk agars showed well defined fluorescent colour combinations across spp. from days 2-5. Fluorescence was best seen on AMA or CMA and the method was extended to screening mixed wild-type samples5-6.

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