Gram-RodCat-

Gram Negative Catalase Negative rods
The Shigella genus is one of the only enterics to be catalase negative, and is the only genus in this key that fits these qualities. The following tests will differentiate between Shigella flexneri and Shigella sonnei.

Tests
Required: SIM media Decarboxylase Ornathine

Key
flexneri Indole + (usually) Decarb Ornathine -

sonnei Indole - Decarb Ornathine +