Phenol Red

Definition

Phenol red is a pH indicator dye commonly used in microbiology to detect changes in the acidity or basicity of a solution. It is particularly useful in identifying microorganisms based on their ability to ferment or metabolize various carbohydrates, which can be observed through color changes in the medium containing phenol red.

5 Must Know Facts For Your Next Test

1. Phenol red changes color from yellow to red as the pH of the solution increases, indicating a more basic environment.
2. The color change of phenol red is commonly used to detect the production of acidic or basic byproducts during microbial fermentation of carbohydrates.
3. Phenol red is often incorporated into microbiological media, such as carbohydrate utilization tests, to identify the metabolic capabilities of different microbial species.
4. The ability of a microorganism to ferment a particular carbohydrate can be determined by observing the color change of the medium containing phenol red.
5. The specific color change observed with phenol red can provide clues about the type of metabolic pathway employed by the microorganism, which is useful for identification and classification purposes.

Review Questions

• Explain how phenol red is used to detect microbial carbohydrate fermentation.
  • Phenol red is a pH indicator dye that is commonly incorporated into microbiological media used to test for the ability of microorganisms to ferment various carbohydrates. When a microorganism metabolizes a carbohydrate, it can produce acidic or basic byproducts that alter the pH of the surrounding medium. These pH changes are then detected by the color shift of the phenol red indicator, allowing for the identification of the microorganism's carbohydrate utilization capabilities.
• Describe how the color change of phenol red can provide information about the type of metabolic pathway employed by a microorganism.
  • The specific color change observed with phenol red can give clues about the metabolic processes used by a microorganism. For example, if the medium containing phenol red turns yellow, it indicates the production of acidic byproducts, suggesting the microorganism is utilizing a fermentative pathway. Conversely, if the medium turns red, it indicates the production of basic byproducts, which may be associated with oxidative metabolic pathways. By observing the color change of phenol red, microbiologists can gain insights into the metabolic capabilities and potential identification of the microorganism under investigation.
• Evaluate the role of phenol red as a tool for the identification and classification of microorganisms.
  • Phenol red is a crucial tool in microbiology for the identification and classification of microorganisms. By incorporating phenol red into microbiological media, researchers can observe the color changes that occur due to the metabolic activities of different microbial species. This information can be used to differentiate between microorganisms based on their ability to ferment specific carbohydrates, which is a key characteristic used in microbial identification and taxonomic classification. The versatility of phenol red as a pH indicator, coupled with its widespread use in various microbiological tests and media, makes it an essential component in the arsenal of tools used by microbiologists to study and characterize the diverse world of microorganisms.

Related terms

pH Indicator: A pH indicator is a chemical compound that changes color in response to changes in the acidity or basicity of a solution, allowing for the determination of the pH.

Carbohydrate Fermentation: Carbohydrate fermentation is the process by which microorganisms break down carbohydrates, such as sugars, to produce energy and various metabolic byproducts, often resulting in changes in the pH of the surrounding medium.

Microbiological Media: Microbiological media are the nutrient-rich substances used to culture and grow microorganisms in the laboratory, often containing various indicators like phenol red to facilitate the identification of microbial species.