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Chapter 12 : Molecular Epidemiology, Ecology, and Evolution of Group A Streptococci

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Abstract:

Within a bacterial species, there are often strains that differ from another in important biological properties. This is certainly the case for (i.e., group A streptococci; GAS), whose members can cause a wide variety of human diseases, yet there does not appear to exist a single omnipotent strain. To better understand strain differences and their relevance to human disease, stable markers have been identified within organisms of this species. Epidemiological markers are useful for investigating outbreaks of disease, and they can also provide a reference point for deciphering the genetic organization of a bacterial population. The epidemiology of a microbial disease is often, in large part, a reflection of the ecology and evolution of the causative agent. For a bacterial species whose world is largely confined to the human population, the selective pressures that most profoundly shape its genetic structure are intrinsic to the human condition. Local microenvironmental conditions can shift during the course of infection within a single host. Also, ecological conditions can vary widely from host to host, and not all exposed hosts are susceptible to infection by a given strain. From the evolutionary standpoint, invasive disease is a dead end for the infecting GAS organism because the severely ill patient becomes immobilized; thus, opportunities for its transmission to new hosts are diminished.

Citation: Bessen D, Hollingshead S. 2006. Molecular Epidemiology, Ecology, and Evolution of Group A Streptococci, p 143-151. In Fischetti V, Novick R, Ferretti J, Portnoy D, Rood J (ed), Gram-Positive Pathogens, Second Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816513.ch12

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Mobile Genetic Elements
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FIGURE 1

Structural features of and -like genes of GAS. Each large box represents an or -like gene, which are arranged in tandem on the chromosome, usually 200 to 300 bp apart. The extent of nucleotide sequence homologies among subregions within and -like genes ranges from highly conserved (open; for regions encoding 5′-end leader peptide and 3′-end cell-associated domains) to highly variable (filled; for regions encoding the determinants of M-serotype). SF forms of the peptidoglycan-spanning coding regions are indicated; five major patterns (A through E) for the content and arrangement of and -like SF gene forms are shown. Other nomenclature that is often used in reference to -like genes includes or (for the SF4 gene), and or (for the downstream -like genes of patterns B through E).

Citation: Bessen D, Hollingshead S. 2006. Molecular Epidemiology, Ecology, and Evolution of Group A Streptococci, p 143-151. In Fischetti V, Novick R, Ferretti J, Portnoy D, Rood J (ed), Gram-Positive Pathogens, Second Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816513.ch12
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