ABSTRACT
Members of this family have a global distribution in soil, water, and vegetation, and comprise part of the gastrointestinal tract flora of humans and animals. Thirty-two genera and more than 130 species have been named. While most species are considered ‘normal flora’ of the gastrointestinal tract, several bona-fide species are enteric pathogens, e.g. Salmonella, Shigella, Yersinia, and various bio/serogroups of Escherichia coli. Salmonella typhi, the agent of typhoid fever, and Yersinia pestis, the plague bacillus, give localized and systemic disease. Most other members play a major role in hospitalacquired (nosocomial) infections.
