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Category: Bacterial Pathogenesis; Clinical Microbiology
Pathogenic Escherichia coli, Shigella, and Salmonella, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816544/9781555812928_Chap14-1.gif /docserver/preview/fulltext/10.1128/9781555816544/9781555812928_Chap14-2.gifAbstract:
The gram-negative enteric pathogens are a closely related group of bacteria. On the basis of genome analyses, Escherichia coli and Shigella can be considered a single species, and their classification as separate genera is largely historical. The Salmonella species are evolutionarily more distant but share many characteristics with the E. coli group. The enteric pathogens usually initiate infection following ingestion, causing diseases ranging from relatively mild enteritis to dysentery and septicemia. The extent of invasion and the nature of the disease depend on the specific set of virulence factors expressed by these pathogens. This chapter discusses the pathogenic members of the enteric bacteria. Many of the iron transport systems originally described in E. coli K-12 are found also in the enteric pathogens. The chapter first talks about siderophore-mediated iron transport systems and nonsiderophore iron transport systems. Next, it summarizes the current state of knowledge with respect to the role of iron transport systems in the pathogenesis of Salmonella, Shigella, and E. coli. Pathogenic E. coli strains are associated with a variety of different diseases and cause both intestinal and extraintestinal infections. While the precise roles of each iron transport system in transmission, colonization, survival, and spread of enteric pathogens in the host cannot be unambiguously defined, several features of iron transport in the enteric pathogens are clear.
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(A) Organization of the enterobactin locus in E. coli, Shigella, and Salmonella. Genes in this cluster are represented by thick arrows. The arrows indicate the direction of transcription and are shaded according to function. The small hatched boxes with right-angle arrows show the location and direction of the Fur binding sequences (not to scale). (B) FepA and EntA amino acid homologies between E. coli K-12 and selected E. coli, Shigella, and Salmonella isolates. The numbers indicate percent identity (percent similarity) to the corresponding E. coli K-12 protein.
(A) Organization of the enterobactin locus in E. coli, Shigella, and Salmonella. Genes in this cluster are represented by thick arrows. The arrows indicate the direction of transcription and are shaded according to function. The small hatched boxes with right-angle arrows show the location and direction of the Fur binding sequences (not to scale). (B) FepA and EntA amino acid homologies between E. coli K-12 and selected E. coli, Shigella, and Salmonella isolates. The numbers indicate percent identity (percent similarity) to the corresponding E. coli K-12 protein.
(A) Structure of the catechol siderophore salmochelin. The molecule containing three DHBS moieties is shown, but two subunits linked by a single glucose also occur. (B) Organization of the iro locus for salmochelin production and transport. The thick arrows indicate the direction of transcription and are shaded according to their roles in biosynthesis or transport. The small hatched boxes with right-angle arrows show the location and direction of the Fur binding sequences (not to scale).
(A) Structure of the catechol siderophore salmochelin. The molecule containing three DHBS moieties is shown, but two subunits linked by a single glucose also occur. (B) Organization of the iro locus for salmochelin production and transport. The thick arrows indicate the direction of transcription and are shaded according to their roles in biosynthesis or transport. The small hatched boxes with right-angle arrows show the location and direction of the Fur binding sequences (not to scale).
(A) Organization of the aerobactin locus in the enteric pathogens. The thick arrows indicate the direction of transcription of each of the open reading frames. The shading of the arrows reflects the function of these genes in aerobactin synthesis or uptake. The small hatched box with a right-angle arrow shows the location and direction of the Fur binding sequence (not to scale). (B) Comparison of the location of the aerobactin locus in selected E. coli isolates and Shigella species. The black boxes represent sequences also found in the E. coli K- 12 genome. These sequences are the likely sites of insertion of the aerobactin island in each strain. The dotted lines delineate DNA of various lengths between the aerobactin locus and the ends of the island. The thick arrows indicate the direction of transcription of the aerobactin genes and are shaded according to the degree of homology of each gene product to the equivalent E. coli pColV-encoded protein.
(A) Organization of the aerobactin locus in the enteric pathogens. The thick arrows indicate the direction of transcription of each of the open reading frames. The shading of the arrows reflects the function of these genes in aerobactin synthesis or uptake. The small hatched box with a right-angle arrow shows the location and direction of the Fur binding sequence (not to scale). (B) Comparison of the location of the aerobactin locus in selected E. coli isolates and Shigella species. The black boxes represent sequences also found in the E. coli K- 12 genome. These sequences are the likely sites of insertion of the aerobactin island in each strain. The dotted lines delineate DNA of various lengths between the aerobactin locus and the ends of the island. The thick arrows indicate the direction of transcription of the aerobactin genes and are shaded according to the degree of homology of each gene product to the equivalent E. coli pColV-encoded protein.
Organization of the S. dysenteriae shu heme transport locus. The thick arrows show the direction of transcription of the shu genes. The shading of the arrows reflects what is known about the role of each shu gene in heme uptake. The hatched boxes with right-angle arrows show the location and direction of the Fur binding sequences (not to scale).
Organization of the S. dysenteriae shu heme transport locus. The thick arrows show the direction of transcription of the shu genes. The shading of the arrows reflects what is known about the role of each shu gene in heme uptake. The hatched boxes with right-angle arrows show the location and direction of the Fur binding sequences (not to scale).
(A) Organization of the sit operon for ferrous iron and manganese uptake. The thick arrows show the direction of transcription of the four sit genes. The small boxes with right-angle arrows show the location and direction of the Fur and MntR binding sites (not to scale). (B) Homology of Sit proteins from selected Salmonella, E. coli, and Shigella isolates to the S. enterica serovar Typhimurium Sit system. The S. flexneri and E. coli CFT073 sitA genes are essentially identical at the nucleotide level; however, an apparent frameshift mutation in the CFT073 sitA gene creates a divergent carboxy terminus in CFT073 SitA.
(A) Organization of the sit operon for ferrous iron and manganese uptake. The thick arrows show the direction of transcription of the four sit genes. The small boxes with right-angle arrows show the location and direction of the Fur and MntR binding sites (not to scale). (B) Homology of Sit proteins from selected Salmonella, E. coli, and Shigella isolates to the S. enterica serovar Typhimurium Sit system. The S. flexneri and E. coli CFT073 sitA genes are essentially identical at the nucleotide level; however, an apparent frameshift mutation in the CFT073 sitA gene creates a divergent carboxy terminus in CFT073 SitA.
The gram-negative enteric pathogens and the diseases they cause
The gram-negative enteric pathogens and the diseases they cause
Iron acquisition systems in the enteric pathogens
Iron acquisition systems in the enteric pathogens