Foodborne Fungal Pathogens And Mycotoxins

It is estimated that some 400 fungi and many of the phytopathogenic ones reduce or threaten the availability and safety of food. From the above, at least 20 are confirmed producers of food related mycotoxins and antinutrients (see: this volume, Chapter 6). Many vegetables, fruits, and seeds lose their nutritive and other qualitative values due to loss of moisture, infection with spoilage microorganisms, and senescence. These types of wastage can occur during transport, handling, and redistribution. Food crops and their products can be infected with single or multiple species of toxigenic fungi. As a result food commodities can be contaminated inadvertently with levels of toxic metabolite(s) often ranging in PPB to PPM levels (Jones et al. 1995; Koshinsky and Khachatourians 1992; Koshinsky and Khachatourians 1994).

Exposure to these metabolites whether singly or in combination results in toxopathological manifestations and even death. Even at subthreshold levels, multiple mycotoxins, by their interactions with multiple sites and targets often produce devastating synergistic effects on living cells and whole animals (Koshinsky and Khachatourians 1992; Koshinsky and Khachatourians 1994; Koshinsky et al. 2000). The historically significant and still prevailing food consumption related threat to public health comes from the fungal alkaloids that lead to ergotism. The fungus, Claviceps purpurea is prevalent in the cool climates where rye is grown. Clavicepes africana has been found to spread through sorghum in North and South America, Australia, and Africa (Bandyopadhyay et al. 1998). Sorghum is the fifth most important cereal crop in the world.

Huge challenges are posed by mycotoxins such as aflatoxins, trichothecenes, and fuminosins that can be addressed by fungal biotechnology. Identification of myco-toxin biosynthesis and their genes, mycotoxin catabolism and biotransformation and their genes could have tremendous value. So far, however, breeding of corn and cereal grain plants through conventional genetics for resistance have been attempted but remains unsuccessful (Medianer 1997). This is possibly due to multiple modes of action of some of these toxins and hence polygenic nature of resistance (Khachatourians 1990; Koshinsky et al. 1998; Woytowich et al. 1997). Perhaps with the isolation of target specific genes a better and fuller resistance could be achieved.

Saprophytic and pathogenic fungi are a major detriment to freshness of fruits and vegetables and safety. Application of antifungal peptides and antimicrobial peptides (Nigam et al. chapter in Arora 2004; Woytowich and Khatchatourians 2001; see: this volume, chapter by Ray and Liewen) could significantly change our options in management of spoilage fungi. A new avenue for applied research is the application of genomics, proteomics, and bioinformatics towards intervention with fungal developmental genes for enhanced functionality, for controlled ingredient delivery, or spoilage of foods. As the knowledge of the regulation of fungal gene expression advances, it is expected that strains will be designed for expression of commodities of high impact in world trade.

Recent advances in diagnostic biotechnology have revolutionized the procedures used in the identification of food fungi. Biochemical identification assays have been miniaturized and through automation and uses of robotics have become faster, reliable, and cost affordable. Rapid identification of fungi and yeasts from foods has become less cumbersome because of ease in sequestering of target fungi from the food ingredients and interfering compounds. In addition, biochemical tests which traditionally have been used in the identification of yeasts and filamentous fungi have been greatly aided by the introduction of polymerase chain reaction (PCR) technology.

Research and development work on understanding of fungal presence in food products and processes are advancing rapidly. For the most part, the goal of research in this area is to decrease process costs. However, fungal biotechnology will enable improvement in health and safety related issues of foods such as better shelf life, decreased threats to human health, and increased perceived healthfulness of the food.

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