The Epsilon test, now commonly known as the Etest, is a method used to determine how sensitive microorganisms like bacteria or fungi are to different antimicrobial drugs.
Understanding the Epsilon Test (Etest)
The Etest, originally called the Epsilometer test, is a way of determining antimicrobial sensitivity by placing a strip impregnated with antimicrobials onto an agar plate. This plate is first spread with a specific strain of bacterium or fungus that is being tested. The test strip has a gradient of the antimicrobial drug along its length, with the highest concentration at one end and the lowest at the other.
As the microorganism grows on the agar plate, it will encounter varying concentrations of the antimicrobial diffusing from the strip. A strain of bacterium or fungus will not grow near a concentration of antibiotic or antifungal if it is sensitive. This creates an elliptical area (zone) where growth is inhibited around the strip.
The point where the edge of this inhibition zone intersects the Etest strip indicates the Minimum Inhibitory Concentration (MIC). The MIC is the lowest concentration of the antimicrobial that prevents the visible growth of the microorganism.
Key Aspects
- Purpose: Determines the sensitivity of bacteria or fungi to antibiotics or antifungals.
- Method: Uses a plastic strip with a pre-defined gradient of an antimicrobial drug.
- Mechanism: Microorganism growth is inhibited in areas where the antimicrobial concentration is sufficient.
- Outcome: Helps determine the Minimum Inhibitory Concentration (MIC), guiding treatment decisions.
This test provides valuable information to healthcare professionals, helping them choose the most effective antimicrobial drug and dosage for treating infections caused by the specific microorganism.
