Dichloran rose-bengal chloramphenicol agar: preferred medium for isolating mycotoxigenic fungal contaminants in silage

This study focuses on selecting an optimal growth medium for isolating mycotoxigenic moulds mainly from maize silage. Therefore, both visually non-mouldy and mouldy samples of maize silage were collected from three farms in Belgium. Additionally, the media were evaluated for one grass silo (mouldy and non-mouldy sample) and two beet pulp silos (mouldy). A statistically significant difference (0.01<P<0.05) between the counts of colony-forming units of moulds on the media was observed for the mouldy maize samples. Dichloran rose-bengal chloramphenicol (DRBC) agar gave high colony count results and high macromorphological diversity for all three silage types. Microscopical and molecular identification experiments showed that Penicillium roqueforti, Penicillium paneum and Aspergillus fumigatus were the most prevalent species, which are all potentially toxigenic fungi. The mycotoxins (roquefortin C, patulin, mycophenolic acid, etc.) impose high risks for animal health and production, as well as for carry-over into animal derived products. In conclusion, DRBC was found to be the medium of choice for isolating and enumerating moulds present in maize silage. The results of this study may serve as a foundation for further research on the increasing problem of mould contamination in silage and may indicate which moulds to focus on in further research regarding mycotoxin contamination of this feed commodity.