Man has been using bacteria for thousands of years, but he has only recently become aware of such uses. Very many foods are made with the aid of bacteria. These micro-organisms modify raw foods and transform them into new products with different chemical, physical, sensory and nutritional characteristics. In addition, these foods have a longer shelf life and sometimes they are even safer to use. Cheese, yoghurt, bread, wine, even dressed pork products and preserves are made with the aid of different species of bacteria. Furthermore, bacteria are used to make a high number of pharmacologically important substances. Actinomycetes, for instance, are thread-like bacteria that morphologically resemble mildews. They are among the most important producers of antibiotics, such as streptomycin and tetracycline.