Shigella dysenteriae

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This page is about microbiologic aspects of the organism(s).  For clinical aspects of the disease, see Shigellosis.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Shigella dysenteriae is a species of the rod-shaped bacterial genus Shigella.[1][page needed] Shigella species can cause shigellosis (bacillary dysentery). Shigellae are Gram-negative, nonspore-forming, facultatively anaerobic, nonmotile bacteria.[2]

S. dysenteriae, spread by contaminated water and food, causes the most severe dysentery because of its potent and deadly Shiga toxin, but other species may also be dysentery agents.[3] Contamination is often caused by bacteria on unwashed hands during food preparation, or soiled hands reaching the mouth.[citation needed]

Diagnosis

Since the typical fecal specimen is not sterile, the use of selective plates is mandatory. XLD agar, DCA agar, or Hektoen enteric agar are inoculated; all give colorless colonies as the organism is not a lactose fermenter. Inoculation of a TSI slant shows an alkaline slant and acidic, but with no gas, or H
2
S
production. Following incubation on SIM, the culture appears nonmotile with no H
2
S
production. Addition of Kovac's reagent to the SIM tube following growth typically indicates no indole formation (serotypes 2, 7, and 8 produce indole[4]).

Shigella flexneri will produce acid and gas from glucose, and Shigella sonnei is mannitol and ornithine positive, and is also a late lactose fermenter (ONPG positive). Some Shigella species can produce indole.

References

  1. Ryan, Kenneth James; Ray, C. George, ed. (2004). Sherris medical microbiology: an introduction to infectious diseases (4th ed.). McGraw-Hill Professional Med/Tech. ISBN 978-0-8385-8529-0.
  2. Hale, Thomas L.; Keusch, Gerald T. (1996). "Shigella: Structure, Classification, and Antigenic Types". In Baron, Samuel. Medical microbiology (4 ed.). Galveston, Texas: University of Texas Medical Branch. ISBN 978-0-9631172-1-2. Retrieved February 11, 2012.
  3. Herold S, Karch H, Schmidt H (2004). "Shiga toxin-encoding bacteriophages—genomes in motion". Int J Med Microbiolo. 294 (2–3): 115–121. doi:10.1016/j.ijmm.2004.06.023. PMID 15493821.
  4. Germani, Y.; Sansonetti, P.J. (2006). "Chapter 3.3.6: The Genus Shigella". In Dworkin, M. (editor-in-chief). The Prokaryotes: Proteobacteria: gamma subclass. 6 (3rd ed.). Springer. pp. 99–122. doi:10.1007/0-387-30746-x_6. ISBN 0-387-25496-X.

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