Medical Laboratory Scientist ASCP Practice Exam 2025 – Complete Study Guide

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What is the lysine reaction result for all species of Citrobacter?

Negative

The lysine reaction result for all species of Citrobacter is considered negative. In microbiology, the lysine decarboxylase test is utilized to determine an organism's ability to decarboxylate lysine, which is associated with the production of alkaline end products and an increase in pH, leading to a color change in the medium.

For Citrobacter species, they typically do not possess the enzyme lysine decarboxylase, which means they do not convert lysine to putrescine and therefore do not produce the alkaline byproducts that would result in a positive reaction. As a result, the medium remains acidic, and no color change occurs, confirming a negative result.

This characteristic is significant in differentiating Citrobacter from other Enterobacteriaceae, which can show variable results. Understanding the biochemical properties of organisms such as Citrobacter is crucial for accurate identification and diagnosis in clinical microbiology.

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Positive

Variable

Indifferent

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