Yeasts

The Good:

Yeasts are microscopic, single-celled fungi. Unlike bacteria, which can thrive on many different types of food, most yeasts can live only on sugars and starches. From these, they produce carbon dioxide gas and alcohol. Thus, they have been useful to man for centuries in the production of foods and beverages such as bread, wine, and beer. Because they can grow under conditions of high salt or sugar content, they can cause the spoilage of certain foods in which bacteria would not grow. Some yeasts are psychrophilic (able to grow at relatively low temperatures), and can create spoilage problems in refrigerated storage areas.

Unlike bacteria, which multiply by binary fission, most yeasts reproduce by a method called budding. A small knob or bud forms on the parent cell, grows and finally separates to become a new yeast dell. Although this is the most common method of reproduction, yeasts also multiply by the formation of spores, and a few yeasts undergo binary fission.

The Bad & The Ugly:

Certain yeasts are pathogenic, e.g. Candida albicans:

Overall however, yeast infections are much less common than are bacterial infections.

Fungal Biology: Understanding the Fungal Lifestyle
by D.H. Jennings, G.Lysek.
A concise introduction to the fundamental properties and activities of fungi in their natural environment. This approach avoids the repetition of taxonomy and life cycle studies found in similar texts. The environmental perspective used to illustrate the book helps readers develop their understanding of basic principles.
(Amazon.co.UK)

Introduction to Modern Mycology
by J.W. Deacon.
Provides students of microbiology, mycology and biology with an introduction to fungi. Emphasizes the behaviour, physiology, activities and practical significance of fungi, and includes extensive sections on fungal pathogens of plants, animals and humans, the roles of fungi in major environmental processes, the use of fungi as biological control agents of pests and pathogens, fungal cell biology, and the application of fungal molecular genetics. Contains numerous photographs, line drawings, and diagrams.
(Amazon.co.UK)