1. Introduction
1.1. Bacteria and microbial diseases
Bacteria, viruses and other microorganisms are found
widely throughout nature and the environment. Bacterial
pathogens are distributed in soil, marine and estuarine
waters, the intestinal tract of animals, or water
contaminated with fecal matter. An average person
carries more than 150 kinds of bacteria which exist
both inside and outside the body (Madigan et al.,
1997). The majority of microorganisms carry out essential
activities in nature, and many are closely associated
with plants or animals in beneficial relations. However,
certain potentially harmful microorganisms can have
profound effects on animals and humans and may be