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Chapter 9 : Gene Acquisition and Loss in the Phylogenetic Lineages of the Invasive Escherichia coli
Category: Bacterial Pathogenesis
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Shigella and enteroinvasive Escherichia coli (EIEC) are a class of enteric pathogens that have evolved the ability to invade epithelial cells and cause severe intestinal illness. In a study on evolutionary analysis of Shigella at the DNA sequence level, the nucleotide sequence of 7,160 bp representing eight housekeeping loci from four regions of the genome was determined. Polymerase chain reaction (PCR) amplification of three marker loci was used to screen for SHI-4, which appeared to be widespread among the clonal groups. Since the isolates used in a study on molecular epidemiology of the Shigella island 4 (SHI-4) PAI were selected on the basis of resistance to multiple antibiotics, it is possible that the actual distribution of these loci among Shigella and EIEC may be different in a randomly sampled collection of strains. Other reports of gene acquisition stem from comparisons of available genome sequences. In contrast to gene acquisition, there is growing evidence that gene loss has been important in the adaptive radiation of Shigella and EIEC. Both gene acquisition and loss have played a major role in the adaptation of these radiations; selection has favored both the establishment of certain virulence factors in particular lineages and the independent deletion of antivirulence functions.
General genetic composition of an invasive E. coli isolate. The pINV plasmid encodes genes involved in host cell entry and it is found in all Shigella and EIEC. The chromosome contains the virR locus, which regulates the acquired pINV plasmid. Example PAIs (SHI-2 and SHI-3) are incorporated in or near tRNA sites. The distribution of PAIs and other virulence loci is variable among the invasive E. coli.
General phylogenetic relationships between the invasive E. coli and other E. coli pathotypes. Patterns of gene acquisition are indicated as follows: * = pINV; square = SHI-1; circle = aerobactin operon; triangle = shuA. The unfilled symbols indicate variable presence of the virulence genes within the group. EAEC, enteroaggregative E. coli; STEC, Shiga toxin-producing E. coli.
Classification of Shigella and EIEC serotypes into phylogenetic groups
PAIs identified in Shigella strains
Invasive E. coli genome sequences publicly available through the NCBI Genomes database