Shigella dysenteriae
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Shigella dysenteriae is a species of the rod-shaped bacterial genus Shigella. Shigella can cause shigellosis (bacillary dysentery). Shigellae are Gram-negative, non-spore-forming, facultatively anaerobic, non-motile bacteria.
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. Contamination is often caused by bacteria on unwashed hands during food preparation, or soiled hands reaching the mouth.
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Signs and Symptoms
The most commonly observed signs associated with Shigella dysentery include colitis, malnutrition, rectal prolapse, tenesmus, reactive arthritis, and CNS problems. Further, Shigella dysenteriae is associated with the development of Hemolytic uremic syndrome, which includes anemia, thrombocytopenia, and renal failure.
Diagnosis
Since the specimen is not sterile, the use of selective plates is mandatory. XLD agar, DCA agar, or HE agar are inoculated and colonies are colorless on all of them as the organism is a non-lactose fermentor. Inoculation of a TSI slant shows an alkaline slant and acidic but with no gas or H2S production. Following incubation on SIM, the culture appears non-motile with no H2S production. Addition of Kovac's reagent to the SIM tube following growth typically indicates no indole formation (serotypes 2, 7 and 8 produce indole).
It's noteworthy that Shigella flexneri will produce acid and gas from glucose, and Shigella sonnei is mannitol and ornithine positive, and is also late lactose fermentor (ONPG positive). Some Shigella species are capable of producing indole.
References
- ^ Ryan, Kenneth James; Ray, C. George, ed. (2004). Sherris medical microbiology: an introduction to infectious diseases (4 ed.). McGraw-Hill Professional Med/Tech. ISBN 978-0-8385-8529-0.
- ^ 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. http://www.ncbi.nlm.nih.gov/books/NBK8038/#A1269. Retrieved February 11, 2012.
- ^ Herold S, Karch H, Schmidt H (2004). "Shiga toxin-encoding bacteriophages--genomes in motion". International Journal of Medical Microbiology 294 (2–3): 115–121. doi:10.1016/j.ijmm.2004.06.023. PMID 15493821.
- ^ Germani, Y.; Sansonetti, P.J. (2006). "Chapter 3.3.6: The Genus Shigella". In Dworkin, M. (editor-in-chief). The Prokaryotes: Proteobacteria: gamma subclass. Volume 6 (3rd ed.). New York: Springer. pp. 99–122. doi:10.1007/0-387-30746-x_6. ISBN 0-387-25496-X.
See also
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