The biochemical profile lactose negative, citrate negative, urease negative, lysine decarboxylase negative, nonmotile best describes which organism?

• A. Proteus vulgaris
• B. Yersinia pestis
• C. Salmonella enterica
• D. Shigella dysenteriae

Answer: (D)

This pattern tests how a bacterium from the Enterobacteriaceae group handles basic nutrient use and movement, which helps separate species by their biochemical traits. Lactose negative means it does not ferment lactose, so we’re looking at nonlactose-fermenting enterics. Citrate negative narrows further, excluding those that can use citrate as a carbon source, such as Klebsiella or Enterobacter. Urease negative rules out urease-producing organisms like Proteus. Lysine decarboxylase negative fits with several nonlactose-fermenters, but the crucial detail is movement: nonmotile eliminates the motile enterics like Salmonella and Proteus. Putting all these clues together points to Shigella dysenteriae, which is lactose nonfermenting, citrate negative, urease negative, lysine decarboxylase negative, and nonmotile.