Antibiotic sensitivity is usually done on?

SJH Nursing Officer - 2019

Applied Microbiology & Infection control

Easy

Appeared in: SJH Nursing Officer - 2019

Explanation

Mueller-Hinton agar is the internationally recommended standard medium for routine antibiotic susceptibility testing (AST), particularly for the Kirby-Bauer disk diffusion method.
Its composition is precisely controlled (e.g., pH, cation content) and it has low levels of antibiotic inhibitors (like thymine and thymidine), which allows for reproducible and reliable measurement of inhibition zones.
It is a non-selective and non-differential medium, meaning it supports the growth of most common, non-fastidious pathogens without introducing variables that could affect test results.

Option A: Blood agar is an enriched medium. The presence of blood can interfere with the diffusion and activity of certain antibiotics, leading to inaccurate sensitivity results.
Option B: MacConkey agar is a selective medium that contains bile salts and crystal violet, which inhibit the growth of Gram-positive bacteria. Therefore, it cannot be used for general susceptibility testing.
Option D: Chocolate agar is a highly enriched medium containing lysed red blood cells. It is not standardized for routine susceptibility testing and is reserved for growing very specific, demanding pathogens.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Standard culture media for antibiotic susceptibility testing as background academic context rather than a clinical decision trigger.
Nurses must understand antibiotic sensitivity reports (antibiograms) to verify that a prescribed antibiotic is effective against the specific bacteria causing a patient's infection. This is a critical step in antibiotic stewardship and preventing treatment failure.
Proper specimen collection (e.g., clean-catch urine, sterile wound swab) is a crucial nursing responsibility. A contaminated sample can lead to the wrong bacteria being identified and tested, resulting in inappropriate and ineffective antibiotic therapy.
What if? If the bacteria isolated was a fastidious organism like Haemophilus influenzae, a specialized test medium (Haemophilus Test Medium), which is a type of Mueller-Hinton agar supplemented with specific growth factors, would be used instead of the standard Mueller-Hinton agar.

How to Approach the Question

Identify the core concept of the question: It asks for the specific, standard medium used for 'antibiotic sensitivity' testing.
Recognize this as a factual recall question from microbiology.
Evaluate each option based on its primary function in a laboratory.
Eliminate Blood agar and Chocolate agar as they are 'enriched' media for growing demanding bacteria, not for standardized testing.
Eliminate MacConkey agar as it is 'selective' and 'differential', meaning it inhibits certain bacteria and is not suitable for general testing.
Recall or deduce that Mueller-Hinton agar is the specifically designed and standardized medium for this purpose, ensuring results are consistent and comparable across different labs.

Concept Tested & Keywords

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