Which organism’s profile is lactose negative, citrate negative, urease negative, lysine decarboxylase negative, and nonmotile?

Which organism’s profile is lactose negative, citrate negative, urease negative, lysine decarboxylase negative, and nonmotile?

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

Answer: (D)

The profile described is a nonfermenter of lactose, negative for citrate utilization, urease, and lysine decarboxylase, plus nonmotile. This combination is classic for Shigella species, particularly Shigella dysenteriae. Lack of lactose fermentation means colonies don’t turn pink on lactose-containing media; a negative citrate test shows it can’t use citrate as a sole carbon source; urease negative indicates no urease activity; lysine decarboxylase negative means it can’t decarboxylate lysine; and being nonmotile helps distinguish it from many other Enterobacteriaceae that are motile, such as Salmonella and Proteus. So the described pattern aligns best with Shigella dysenteriae.

The profile described is a nonfermenter of lactose, negative for citrate utilization, urease, and lysine decarboxylase, plus nonmotile. This combination is classic for Shigella species, particularly Shigella dysenteriae. Lack of lactose fermentation means colonies don’t turn pink on lactose-containing media; a negative citrate test shows it can’t use citrate as a sole carbon source; urease negative indicates no urease activity; lysine decarboxylase negative means it can’t decarboxylate lysine; and being nonmotile helps distinguish it from many other Enterobacteriaceae that are motile, such as Salmonella and Proteus. So the described pattern aligns best with Shigella dysenteriae.