ABSTRACT
Plague is caused by the bacterium Yersinia pestis (Figure 2.1). The Yersinia genus contains over 13 species, most of which do not cause human illness or do so rarely. Unfortunately, there are three species that cause human disease: Y. enterocolitica and Y. pseudotuberculosis cause primarily foodborne diseases and are discussed in Chapter 10. The other human pathogen is Y. pestis, which causes plague and is the subject of this chapter. These bacteria are Gram negative, which means that the bacteria do not exhibit a purple color when Gram stain is applied; this trait is one of the methods used to distinguish among different species of bacteria. Y. pestis is capable of movement when grown at 77°F (25°C), but not at human body temperature (98.6°F or 35°C) (Prentice 2011).
