In this age, societies take great pains to protect their populations against exposure to undesirable microbes. Pasteurization, sterilization, sanitation and HACCP procedures have been instrumental in this effort, particularly for gastro-intestinal diseases. We are therefore much less exposed to microbes, good or bad, than in ancient times. An important feature of this book is the exploration of Escherichia coli as a probiotic culture. This is very much forward thinking, and challenges the current paradigm. Indeed, probiotics have mainly been selected from lactic cultures, and exploring the use of coliforms has novelty. Another important feature of this book is the development of an automated assay for the evaluation of interactions between probiotics and pathogens. The agarose-supernatant strategy is a novel development of the microplate systems which has great potential for rapid screening of effective cultures.