Chapter 7 : Molecular Epidemiology and Population Genetics of Extraintestinal Pathogenic

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The strains of that cause such extraintestinal infection, in whatever host species, have long been recognized to differ, collectively, from those that colonize the intestinal tract or cause diarrhea in members of the same species. Such strains have been the subject of considerable study in an effort to better understand their distinguishing features, virulence mechanisms, host and syndrome range, evolutionary origins, reservoirs, and transmission pathways. This has led to the creation of various taxonomic categories and commensals. Such labels imply that the special ability of these strains to cause extraintestinal disease is their raison d'être. Several broad generalizations can be made regarding the distribution of virulence factors among individual extraintestinal pathogenic (ExPEC) strains. First, ExPEC strains typically express representatives of multiple different functional categories of virulence factors. Second, ExPEC strains commonly display multiple representatives of a particular functional class of virulence factors. Third, different ExPEC strains exhibit radically different combinations of virulence factors, evidence that multiple genotypes can cause extraintestinal virulence. An important aspect of virulence genes, aside from presence/absence and expression, is point mutations. In contrast, pulsed-field gel electrophoresis (PFGE) analysis, which is relatively insensitive to broad phylogenetic relationships, provides resolution down to the level of individual clones within the larger clonal groups. Better understandings of ExPEC strains’ pathogenetic mechanisms, fecal reservoirs, transmission pathways, antimicrobial resistance development, and evolutionary origins are needed to guide the development of effective preventive measures against these important opportunistic pathogens.

Citation: Johnson J. 2011. Molecular Epidemiology and Population Genetics of Extraintestinal Pathogenic , p 91-107. In Walk S, Feng P (ed), Population Genetics of Bacteria. ASM Press, Washington, DC. doi: 10.1128/9781555817114.ch7
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Image of Figure 1.
Figure 1.

Diagram of a representative ExPEC cell and its virulence factors. Small solid circles, triangles, and rectangles represent membrane-associated proteins that contribute to complement resistance (serum survival), host cell invasion, and other virulence-promoting functions. LPS, lipopolysaccharide. Adapted with permission from reference .

Citation: Johnson J. 2011. Molecular Epidemiology and Population Genetics of Extraintestinal Pathogenic , p 91-107. In Walk S, Feng P (ed), Population Genetics of Bacteria. ASM Press, Washington, DC. doi: 10.1128/9781555817114.ch7
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Image of Figure 2.
Figure 2.

Phylogenetic distribution of extraintestinal virulence genes in relation to clinical source. Dendrogram at left depicts phylogenetic relationships for the 72 members of the Reference (ECOR) collection, as inferred based on MLEE using 38 metabolic enzymes ( ). The four major phylogenetic groups (A, B1, B2, and D) of and the nonaligned strains (“non”) are bracketed and labeled. Bullets at right indicate presence of putative virulence genes (, P fimbriae; , group II capsule synthesis; , S and F1C fimbriae; , aerobactin receptor; , serum resistance; and , type 1 fimbriae). Horizontal bars at right indicate the 10 ECOR strains that are symptomatic infection isolates, all from humans with UTI. The remaining strains, except for one asymptomatic bacteriuria isolate, are fecal isolates from healthy human or animal hosts. Note the concentration of (chromosomal) virulence genes , , and within phylogenetic groups B2 and D, but their occasional joint appearance also in distant lineages, consistent with coordinate horizontal transfer. The more scattered phylogenetic distribution of is consistent with this gene’s plasmid location, whereas is nearly universally prevalent, consistent with its presence in other species of , presumably reflecting an origin in a shared enterobacterial ancestor. Note the concentration of UTI isolates within phylogenetic groups B2 and D, and the association of virulence genes with the UTI isolates. Neighbor joining tree dendrogram adapted with permission from reference . Entirety of figure and legend reprinted with permission from reference .

Citation: Johnson J. 2011. Molecular Epidemiology and Population Genetics of Extraintestinal Pathogenic , p 91-107. In Walk S, Feng P (ed), Population Genetics of Bacteria. ASM Press, Washington, DC. doi: 10.1128/9781555817114.ch7
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