An investigation of fungal contamination on the surface of medicinal herbs in China

With the popular and extensive use of medicinal herbs all over the world, safety issues related to the contamination with microbial organisms has become a major concern [1–4]. Most of fungi are toxigenic in nature, and some other non-toxigenic species may impart a mouldy odour and taste [5]. In the pre-harvest stage, medicinal herbs are susceptible to indigenous fungi in the soil where they were grown. The dried part of medicinal herbs may be exposed to fungal contamination during post-harvest. Different taxonomic groups of fungi were detected in medicinal plant samples collected from different regions, suggesting Aspergillus and Penicillium groups as the most predominant genera [6–8]. Many species of Aspergillus and Penicillium genera are known mycotoxin-producers, which may pose a great threat to public health [5].

Mycotoxigenic fungi could produce a wide variety of mycotoxins. Aflatoxins (B₁, B₂, G₁, and G₂) are a family of structurally related toxic secondary metabolites which mainly produced by certain strains of Aspergillus flavus (A. flavus) and Aspergillus Parasiticus (A. parasiticus) [9, 10]. Aflatoxin B₁ (AFB₁) was classified as a Group I carcinogen by the World Health Organization for Research on Cancer in 1993 [11]. Sterigmatocystin (ST), the stable intermediate in the final steps of aflatoxin biosynthesis in the aflatoxin-producing fungi A. flavus and A. parasiticus, was proven to be another carcinogenic mycotoxin [12]. Some certain stains, e.g., A. versicolor, A. sydowi, A. nidulans, Bipolaris, Chaetomium and Emericella spp. could also produce ST [13–16]. Produced by P. verrucosum, P. nordicum and A. carbonarius [17–19], another mycotoxin ochratoxin A (OTA) could cause a series of adverse effects in animals and humans, including teratogenicity, immunotoxicity, genotoxicity and mutagenicity [20–22].

This study aimed to investigate the presence of fungi on the surface of 45 medicinal herbs samples of fifteen herbs collected from Hunan, Hubei and Guangxi Province, China, by the characterization of morphology and ITS sequencing, followed by analysis of mycotoxigenic potential of isolated fungi using LC-MS/MS for the measurement of AFB₁, AFB₂, AFG₁, AFG₂, ST and OTA.