Definitions

shigellae

Shigella dysenteriae

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.

Diagnosis

A stool specimen is Gram-stained to show G - ve, rods, with no particular arrangement. Enrichment is performed by growing the organisms on Selenite-F broth. Then, 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 non-lactose fermentor. TSI slant would show a profile of (K/A/H2S-/g-), and SIM would appear (+/-/+).

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 indol.

References

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