TAILIEUCHUNG - Chapter 147. Shigellosis

The discovery of Shigella as the etiologic agent of dysentery—a clinical syndrome of fever, intestinal cramps, and frequent passage of small, bloody, mucopurulent stools—is attributed to the Japanese microbiologist Kiyoshi Shiga, who isolated the Shiga bacillus (now known as Shigella dysenteriae type 1) from patients' stools in 1897 during a large and devastating dysentery epidemic. Shigella cannot be distinguished from Escherichia coli by DNA hybridization and remains a separate species only on historical and clinical grounds. Definition Shigella is a non-spore-forming, gram-negative bacterium that, unlike E. coli, is nonmotile and does not produce gas from sugars, decarboxylate lysine, or. | Chapter 147. Shigellosis The discovery of Shigella as the etiologic agent of dysentery a clinical syndrome of fever intestinal cramps and frequent passage of small bloody mucopurulent stools is attributed to the Japanese microbiologist Kiyoshi Shiga who isolated the Shiga bacillus now known as Shigella dysenteriae type 1 from patients stools in 1897 during a large and devastating dysentery epidemic. Shigella cannot be distinguished from Escherichia coli by DNA hybridization and remains a separate species only on historical and clinical grounds. Definition Shigella is a non-spore-forming gram-negative bacterium that unlike E. coli is nonmotile and does not produce gas from sugars decarboxylate lysine or hydrolyze arginine. Some serovars produce indole and occasional strains utilize sodium acetate. S. dysenteriae S. flexneri S. boydii and S. sonnei serogroups A B C and D respectively can be differentiated on the basis of biochemical and serologic characteristics. Genome sequencing of E. coli K12 S. flexneri 2a S. sonnei S. dysenteriae type 1 and S. boydii has revealed that these species have 93 of genes in common. The three major genomic quot signatures quot of Shigella are 1 a 215-kb virulence plasmid that carries most of the genes required for pathogenicity particularly invasive capacity 2 the lack or alteration of genetic sequences encoding products . lysine decarboxylase that if expressed would attenuate pathogenicity and 3 in S. dysenteriae type 1 the presence of genes encoding Shiga toxin a potent cytotoxin. Epidemiology The human intestinal tract represents the major reservoir of Shigella which is also found albeit rarely in the higher primates. Because excretion of shigellae is greatest in the acute phase of disease the bacteria are transmitted most efficiently by the fecal-oral route. Most cases of shigellosis are caused by person-to-person transmission although some outbreaks reflect contamination of water or food. Shigella can also be transmitted by .

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