Antagonistic relationships between lactic acid bacteria and main bacterial and fungal food contaminants

Abstract

Food contamination is the origin of important economic losses and of illness in millions of people every year. It is mainly caused by fungi and bacteria which, in some cases, apart from spoiling food, produce toxins that harm consumers, and spores that can elicit allergic reactions. It is especially concerning in developing countries, where the lack of resources and food safety controls, together with malnutrition, make individuals particularly vulnerable. To solve this problem, the application of microorganisms or of the compounds they produce to food, which is known as “biopreservation”, is receiving increasing attention. Lactic acid bacteria (LAB) are of very much interest in this field, as most of the species are considered to be safe for human consumption and have been previously reported to present inhibitory activities against important pathogens in many scientific papers. In this Master Thesis, we propose their use for preservation of nutritional formula for malnourished kids in developing countries. For this reason, firstly, the inhibitory potential of Lactobacillus plantarum CECT 8962 against Penicillium expansum CECT 2278 was studied in this product. It was observed that nutritional formula was a complex environment where some Bacillus spp. could also grow, that these species were responsible for the inhibition of the fungus, and that L. plantarum CECT 8962 had a strong antagonistic activity over them. Due to these observations, it was decided to also assess the effect of an array of LAB strains on the growth of different Bacillus that are frequent food contaminants, and the effect of those Bacillus over important fungal pathogens. Clear inhibition by Bacillus was observed over fungi, both in co-culture and when using Bacillus supernatants, in most of the cases. Regarding LAB and Bacillus, however, inhibitory activities where only demonstrated in the case of some co-cultures.