What single biochemical test result distinguishes gamma-proteobacteria in the family Enterobacteriaceae from gammaproteobacteria in the family Pasteurellaceae?

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Step 1: Understand the two bacterial families involved: Enterobacteriaceae and Pasteurellaceae, both belonging to the class Gammaproteobacteria but differing in certain biochemical characteristics.

Step 2: Recall that Enterobacteriaceae are typically facultative anaerobes that ferment glucose and often produce the enzyme catalase, while Pasteurellaceae have different metabolic profiles and enzyme activities.

Step 3: Identify common biochemical tests used to differentiate bacterial families, such as oxidase test, catalase test, fermentation tests, and others.

Step 4: Focus on the oxidase test, which detects the presence of cytochrome c oxidase enzyme. Enterobacteriaceae are generally oxidase-negative, whereas Pasteurellaceae are oxidase-positive.

Step 5: Conclude that the oxidase test result is the key biochemical test that distinguishes Enterobacteriaceae (oxidase-negative) from Pasteurellaceae (oxidase-positive).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Gamma-proteobacteria Classification

Gamma-proteobacteria is a diverse class of Gram-negative bacteria that includes several families such as Enterobacteriaceae and Pasteurellaceae. Understanding their classification helps in identifying differences in metabolic and biochemical traits used for bacterial identification.

Biochemical Tests in Bacterial Identification

Biochemical tests detect specific enzymatic activities or metabolic capabilities of bacteria, serving as key tools to differentiate closely related groups. These tests include assays for enzymes like oxidase and catalase, which reveal functional differences between bacterial families.

Oxidase Test Differentiation

The oxidase test detects the presence of cytochrome c oxidase enzyme. Enterobacteriaceae are typically oxidase-negative, while Pasteurellaceae are oxidase-positive. This single test effectively distinguishes these two families within gamma-proteobacteria.

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Textbook Question

Which of the following is a bile-tolerant anaerobe?

a. Bacteroides

b. Escherichia

c. Shigella

d. Prevotella

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