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Chapter 15 : Impact of Horizontal Gene Transfer on the Evolution of Pathogenesis

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Abstract:

The establishment of a phylogenetic tree is a prerequisite for studying the evolution of virulence. The current nomenclature of the genus is based on this phylogenetic tree and distinguishes only two species: and . If acquisition of SPI-1 introduced a virulence factor required for the pathogenesis of diarrheal disease, then mutational inactivation of this determinant should attenuate serotypes in animal models of gastroenteritis. The contribution of the invasion-associated type III secretion system to serotype Typhimurium pathogenesis in this animal model has recently been investigated using strains carrying mutations in and . The majority of antibodies elicited by immunization with heat-killed serotype Typhimurium or with a live-attenuated serotype Typhimurium vaccine is directed against the immunodominant O-antigen. Mathematical models predict that in this between-serotype competition, the serotype with higher transmissibility will dominate and eventually eliminate its competitor. The generation of O-antigen polymorphism through horizontal gene transfer was therefore a likely mechanism that allowed serotypes to adapt to the enhanced immune memory encountered in warm-blooded hosts. The gene is present in biphasic subspecies but absent from monophasic subspecies and , suggesting its acquisition by horizontal gene transfer. A primary pathogen can be defined as an organism capable of entering a host and finding a unique niche to multiply and avoid or subvert the host defenses, the outcome of which may be clinical disease manifestations.

Citation: Kingsley R, Townsend S, Norris T, Bäumler A, Tsolis R, Ficht T, Adams L. 2000. Impact of Horizontal Gene Transfer on the Evolution of Pathogenesis, p 227-240. In Brogden K, Roth J, Stanton T, Bolin C, Minion F, Wannemuehler M (ed), Virulence Mechanisms of Bacterial Pathogens, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555818111.ch15

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FIGURE 1

The evolution of dysenterylike disease. The branching structure of the phylogenetic tree shown on the left is based on comparative sequence analysis of housekeeping genes (reported previously) ( ). Calibration of the phylogenetic tree of and the genus using a molecular clock has been performed recently ( ). The phylogenetic distribution of SPI-1 genes among and subspecies has been described by Selander and coworkers ( ). Aleksic et al. reported on the ability of and serotypes to cause a dysenterylike disease in humans ( ). The lineages in which SPI-1 and the virulence plasmid were acquired have been postulated by Ochman and Groisman and are indicated by arrows ( ).

Citation: Kingsley R, Townsend S, Norris T, Bäumler A, Tsolis R, Ficht T, Adams L. 2000. Impact of Horizontal Gene Transfer on the Evolution of Pathogenesis, p 227-240. In Brogden K, Roth J, Stanton T, Bolin C, Minion F, Wannemuehler M (ed), Virulence Mechanisms of Bacterial Pathogens, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555818111.ch15
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Image of FIGURE 2
FIGURE 2

Evolution of systemic disease caused by serotypes. The branching structure of the phylogenetic tree shown on the left is based on comparative sequence analysis of housekeeping genes (reported previously) ( ). The phylogenetic distribution of SPI-2 has been described recently ( ), suggesting its acquisition by a lineage ancestral to (arrow). Boyd and coworkers determined the scattered phylogenetic distribution of the gene cluster ( ). Aleksic et al. reported on the ability of and serotypes to cause extraintestinal infections in humans ( ).

Citation: Kingsley R, Townsend S, Norris T, Bäumler A, Tsolis R, Ficht T, Adams L. 2000. Impact of Horizontal Gene Transfer on the Evolution of Pathogenesis, p 227-240. In Brogden K, Roth J, Stanton T, Bolin C, Minion F, Wannemuehler M (ed), Virulence Mechanisms of Bacterial Pathogens, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555818111.ch15
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Image of FIGURE 3
FIGURE 3

Adaptations of serotypes to circulate in populations of warmblooded vertebrates. The branching structure of the phylogenetic tree shown on the left is based on comparative sequence analysis of housekeeping genes (reported previously) ( ). The phylogenetic distributions of and have been determined recently ( ; Kingsley et al., submitted). The H-antigens of monophasic and biphasic serotypes are reviewed by Kelterborn ( ). Aleksic et al. have reported on the frequency of and serotype isolation from clinical infections ( ). , The article by Aleksic et al. does not distinguish between subspecies IV and VII.

Citation: Kingsley R, Townsend S, Norris T, Bäumler A, Tsolis R, Ficht T, Adams L. 2000. Impact of Horizontal Gene Transfer on the Evolution of Pathogenesis, p 227-240. In Brogden K, Roth J, Stanton T, Bolin C, Minion F, Wannemuehler M (ed), Virulence Mechanisms of Bacterial Pathogens, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555818111.ch15
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