Pro-technological, probiotic, pathogenic and spoilage microorganisms and their role in food ecosystems. Microorganisms as indicators of food quality and safety. Role of microorganisms as starter in the production of fermented foods and in the enhancement of the organoleptic characteristics and health content of the final products. Sources of microbial contamination (air, soil, water, plants, animal, human). Food infection: enteropathogenic Escherichia coli, Salmonella, Shigella, Yersinia enterocolitica, Vibrio, Campylobacter jejuni, Brucella, Listeria monocytogenes. Food intoxication: Clostridium botulinum, Staphylococcus aureus. Foodborne toxicoinfections: Clostridium perfringens, Bacillus cereus. General characteristics of micotoxigenic fungi and mycotoxins.