Which of the following organisms is urease positive?

Nocardia is recognized as urease positive, which means it can hydrolyze urea to ammonia and carbon dioxide due to the presence of the enzyme urease. This biochemical characteristic is particularly important in differentiating Nocardia from other organisms in clinical microbiology.

Nocardia species are aerobic actinomycetes and can be found in soil and water, and they are known to cause opportunistic infections in immunocompromised individuals. The urease test is often used in identifying and differentiating Nocardia from other pathogens due to its ability to produce urease, leading to an increase in the pH of the medium, which can be observed as a color change.

In contrast, Salmonella and Shigella are generally urease negative and typically do not produce this enzyme, which can be critical for identification in laboratory settings. Moraxella is also urease negative, reinforcing the significance of urease production as a characteristic of Nocardia. Understanding the urease status of these organisms is essential for accurate microbial identification and subsequent treatment decisions.