Citrate and Urease

These flashcards cover the key concepts surrounding the Simons citrate and urease tests, their components, and interpretations of the results.

Simons Citrate Test

Screens bacterial isolates for the ability to utilize citrate as its sole carbon and energy source.

Positive Citrate Test

Indicates the generation of alkaline byproducts from citrate metabolism, shown by a color change in the pH indicator.

Sodium Citrate

The sole carbon source in the citrate medium.

Ammonium Phosphate

The sole nitrogen source used in the citrate medium.

Bromothymol Blue

A pH indicator used in citrate testing; turns blue in alkaline conditions.

Color Change Interpretation - Blue

Indicates a positive result for citrate use, as the increase in pH results from ammonia production.

Color Change Interpretation - Green

Indicates a negative result for citrate use, either no growth or no color change.

Growth with No Color Change

Indicates a positive result, as bacterial growth suggests citrate use, even if pH hasn't changed yet.

Urease Test Purpose

Identifies organisms that can hydrolyze urea to produce ammonia and carbon dioxide.

Urease Media Components

Contains urea and phenol red as pH indicator for detecting urease activity.

Phenol Red Color Change - Yellow

Indicates acidic conditions and a negative urease test.

Phenol Red Color Change - Pink/Fuchsia

Indicates alkaline conditions, confirming the presence of urease enzyme.

Positive Urease Test Examples

Organisms like Proteus mirabilis and Proteus vulgaris that show bright pink color change.

Negative Urease Test Examples

E. coli and Salmonella, which do not change color due to absence of urease enzyme.