Probiotics are live microbes that can be formulated into many different types of products, including foods, drugs, and dietary supplements. Species of Lactobacillus and Bifidobacterium are most commonly used as probiotics, but the yeast Saccharomyces cerevisiae and some E. coli and Bacillus species are also used as probiotics. Lactic acid bacteria (LAB), including species of Lactobacillus, which have been used for preservation of food by fermentation for thousands of years, can serve a dual function by acting as agents of food fermentation and, in addition, potentially imparting health benefits. Strictly speaking, however, the term "probiotic" should be reserved for live microbes that have been shown in controlled human studies to impart a health benefit. Fermentation of food provides characteristic taste profiles and lowers the pH, which prevents contamination by potential pathogens. Fermentation is globally applied in the preservation of a range of raw agricultural materials (cereals, roots, tubers, fruit and vegetables, milk, meat, fish etc.).