from PART III - Paradigms of Bacterial Evolution
Published online by Cambridge University Press: 16 September 2009
INTRODUCTION
Acquisition of genetic elements by horizontal transfer has played a major role in the evolution, virulence, and transmission of many bacteria. The genus Yersinia represents a very good example of a bacterial group whose pathogenicity and transmission progressively evolved with the gradual acquisition of foreign genetic elements.
Yersinia are Gram-negative bacteria that belong to the family Enterobacteriaceae. The genus is composed of 12 species that can be differentiated into pathogenic (Y. pseudotuberculosis, Y. enterocolitica, and Y. pestis) and non-pathogenic (Y. intermedia, Y. kristensenii, Y. fredericksenii, Y. aldovae, Y. rohdei, Y. bercovieri, Y. mollaretii, and Y. aleksiciae) species (Figure 8.1; see also color plate after p. 174). Y. ruckeri is not discussed here because the inclusion of this fish pathogen in the genus Yersinia is still controversial. Like several other species of Enterobacteriaceae, Y. enterocolitica and Y. pseudotuberculosis are true enteropathogens, while Y. pestis is the causative agent of plague. This chapter focuses on the evolution and lateral gene transfer in these three pathogenic species.
Y. enterocolitica and Y. pseudotuberculosis are widely spread in countries with temperate climates. They are transmitted by the fecal-oral route and cause intestinal symptoms such as abdominal pain (especially Y. pseudotuberculosis), diarrhea (especially Y. enterocolitica), and fever, usually of moderate intensity.
The species Y. enterocolitica is subdivided into six biotypes (1A, 1B, and 2 to 5). All strains are pathogenic except those of biotype 1A. Pathogenic Y. enterocolitica can be further subdivided into low- and high-pathogenicity strains.
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