An organism that is both urease and PD negative, with specific TSIA results, is being tested. Which organism is being described?

The organism being described as both urease and PD (phenylalanine deaminase) negative, along with specific Triple Sugar Iron Agar (TSIA) results, is indicative of Shigella spp.

Shigella species are known for their lack of urease production and their ability to be tested as phenylalanine deaminase negative. These characteristics help differentiate them from other enteric organisms that may demonstrate urease activity or produce phenylalanine deaminase. Furthermore, when examined using TSIA, Shigella typically shows a yellow slant and yellow butt, indicating glucose fermentation without gas or hydrogen sulfide production. This profile is crucial because it helps microbiologists and pathologists identify Shigella in laboratory settings efficiently.

Thus, the combination of being urease negative and PD negative aligns with the biochemical profile for Shigella, making it the correct identification for the organism in question.