What is the name of the medium that changes color when bacterium grows in it?

RUHS, Jaipur, PB B.Sc Nursing Entrance-2019

Applied Microbiology & Infection control

Easy

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2019

Explanation

An indicator medium (or differential medium) is specifically designed to distinguish between different microorganisms growing on the same medium.
It contains chemical indicators, such as pH-sensitive dyes (e.g., neutral red, phenol red), that change color in response to the specific metabolic byproducts of bacteria.
A classic example is the fermentation of a sugar, which produces acid, lowers the pH, and triggers a color change in the indicator, thus differentiating fermenters from non-fermenters.

Option A: Enriched media are designed to support the growth of fastidious (nutritionally demanding) bacteria by providing extra nutrients like blood or serum. Their primary purpose is growth, not differentiation by color change.
Option B: Enrichment media are typically liquid broths used to increase the population of a specific target organism in a mixed sample, often by inhibiting the growth of other organisms. It does not rely on a color change for differentiation.
Option C: A selective medium's main function is to suppress the growth of unwanted microorganisms while allowing the desired ones to grow. While many media are both selective and differential (like MacConkey agar), the defining characteristic of a selective medium is inhibition, not the color change itself.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Types and functions of bacterial culture media as background academic context rather than a clinical decision trigger.
In clinical laboratories, indicator media are crucial for the rapid presumptive identification of pathogens from patient specimens (e.g., urine, stool, wound swabs).
For instance, plating a urine sample on MacConkey agar can quickly differentiate lactose-fermenting E. coli (pink colonies), a common cause of UTIs, from non-lactose fermenters like Pseudomonas (colorless colonies).
This rapid differentiation guides the choice of subsequent identification tests and can influence initial antibiotic therapy.

How to Approach the Question

This is a factual recall question based on definitions in microbiology.
Identify the key phrase in the question: 'changes color when bacterium grows'.
Analyze the function implied by each option's name.
An 'indicator' is something that provides a visible sign. Therefore, an 'indicator medium' logically is one that provides a visual sign, like a color change.
Contrast this with the other terms: 'Enriched' implies adding nutrients, 'Enrichment' implies increasing concentration, and 'Selective' implies choosing which bacteria can grow.
Based on this analysis, the term 'Indicator medium' directly matches the function described in the question.

Concept Tested & Keywords

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E6 Microbiology Applied AnjuDhir 3e Part 1 p. 114-116

E6 Microbiology Essentials Sastry 4e Part 1 pp. 48-50, 49-51