Binding of aflatoxin B1 to lactic acid bacteria and Saccharomyces cerevisiae in vitro: A useful model to determine the most efficient microorganism

Abstract

Mycotoxins are toxic fungal metabolites found as contaminants in many agricultural products. Feeds contaminated with mycotoxins have a health risk to animals and, as a consequence, may cause big economical losses due to the low efficacy of animal husbandry (Richard, 2007). In addition, directly or indirectly (animal by-products) contaminated foods may also have a health risk to humans (CAST, 2003; Hussein & Brasel, 2001; Wild, 2007). Aflatoxins (AFs), a group of potent mycotoxins with mutagnic, carcinogenic, teratogenic, hepatotoxic and immunosupresive properties, are of particular importance because of their major occurrence and adverse effects on animal and human health, generalized as ?aflatoxicosis? (CAST, 2003; Hussein & Brasel, 2001; Magnoli et al., 2011). The AFs are produced by genus Aspergillus, mainly A. flavus, A. parasiticus and A. nomius, that grow on a variety of raw material during growth, harvest, storage and transportation of for example, the cereal used in the preparation of food and feed commodities (Ito et al., 2001; Kurtzman et al., 1987; Payne, 1998; Pereyra et al., 2010). The investigation of strategies to prevent the presence of AFs in foods, as well as, to eliminate, inactivate or reduce the bio-availability of these mycotoxins in contaminated products include physical, chemical, and biological methods (Bueno et al., 2001; CAST, 2003; Kabak et al., 2006). Limitations such as the loss of nutritional and sensory qualities of the product, the expensive equipment required for these techniques and the impossibility to guarantee the desired results, have allowed us to consider the hipothesis that foods and feeds can always be potentially contaminated with aflatoxins. For instance, in the poultry industry aflatoxin B1 (AFB1) is almost an unavoidable feed contaminant and levels from 0-200 ng/g have been reported (Dalcero et al., 1997). On the other hand, it is known that lactic acid bacteria (LAB) and some yeast, principally Saccharomyces cerevisiae, are capable to bind AFs in liquid media, apparently to cell wall components, polysaccharides and peptidoglycans of LAB (Haskard et al., 2001; Latinen et al., 2004) and glucomannans of yeast (Karaman et al., 2005; Raju & Devegowda 2000) and therefore could be used as potential mycotoxin decontaminating (Armando et al 2011; El-Nezami et al., 1998; Haskard et al., 2000, 2001; Hernandez-Mendoza et al., 2009; Lee et al., 2003; Peltonen et al., 2001; Shetty et al., 2007). The inclusion of appropriate microorganisms in the contaminated diet could prevent the absorption of mycotoxins during their passage in the gastrointestinal tract and eliminated in the faeces (Bueno et al., 2007; El-Nezami et al., 2000; Gratz et al., 2004; Gratz et al., 2007). Moreover, Kankaanpää et al. (2000) showed that the binding of AFB1 to the surface of LAB reduced their adhesive properties, and the accumulation of aflatoxins in the intestine may therefore be reduced via the increased excretion of an aflatoxin-bacteria complex. These considerations encouraged the recent emphasis on biological methods, but mainly focused on preventing AFs absorption in the gastrointestinal tract of the consumers, including these microorganisms in the diet and so prevent the aflatoxicosis effects. The first step in this direction is the selection of the most efficient microorganism for AFB1 removing and while many researchers have assayed LAB and yeast with AFB1 binding abilities (Ciegler et al., 1966; El-Nezami et al., 1998; Gourama & Bullerman, 1995; Haskard et al., 2001; Line et al., 1994; Oatley et al., 2000) no clear mechanism for this effect has been provided. Thus, this selection frequently is performed using a single concentration of AFB1, but we demonstrated that the microorganism efficiency may change when the mycotoxin concentration is modified (Bueno et al., 2007; Pizzolitto, 2011), therefore the microorganism selected could not be the most competent. In this context, we investigated the nature of the interaction between different microorganisms and AFB1 molecule, which led us to develop a model to explain the binding of AFB1 by LAB and Saccharomyces cerevisiae strains. This model allows an estimation of two important parameters related to a microorganism´s capacity for dietary decontamination: the number of binding sites for AFB1 in the surface microorganism (M) and the equilibrium constant of the process involved (Keq), both of them are useful in the selection of the most suitable microorganism in a wide range of AFB1 concentration (Bueno et al., 2007). In adittion, studies of viability of the microorganisms in the salivary and gastrointestinal tract, cell adhesion, autoaggregation, coaggregation and antimicrobial activity against pathogen strains, were also evaluated as a way to research potential beneficial properties on the host (Armando et al., 2011). Thus, in this chapter we describe the development and application of an in vitro methodology to evaluate the aflatoxin B1 binding ability, gastrointestinal tolerance and potential beneficial properties of Saccharomyces cerevisiae strains, useful to select the more appropriated microorganism to be assayed in expensive, complicated but necessary in vivo studies.