This new book brings together for the first time a world-class series of experts to explore this intricate system. These scientists and clinicians explore the traditional bacteriological and novel molecular techniques, which are now being used to define previously unknown bacterial species. The nature of bacterial epithelial interactions in health and disease is investigated. Specific defence mechanisms such as defensins, the epithelial immune system and cytokine regulation are covered. The modification of this bacterial environment may have a valuable role in preventing and treating disease - the effects of prebiotics, food, and probiotic bacteria are defined. Lastly, the areas of proven clinical benefit from the use of probiotic bacteria, and their mechanisms of action, are discussed.