Resistance phenotype testing Principle of E-Test E test is a quantitative technique that is based on combination of concept of both dilution and diffusion principle for susceptibility testing. E test strip is placed on to an inoculated agar plate; there is an immediate release of antibiotics from the plastic carrier surface into the agar surface. After incubation, bacterial growth becomes visible, symmetrical inhibition ellipse along the strip is seen. Purpose of E-Test Determine the MIC of fastidious, slow-growing or nutritionally deficient micro-organisms, or for a specific type of patient or infection.
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Emulsify 3 or 4 individual test strain colonies and transfer to a tube of saline. Compare turbidity to that in the 0. Adjust turbidity of inoculum to match that standard. Streak the swab over the entire surface of the agar plate by rotating the plate approximately 60o.
Complete inoculation by running the swab around the rim of the agar. Leave the lid of the plate ajar for 5 minutes no more than 15 minutes to allow any excess moisture to be absorbed before applying strips. NOTE: Swab plate within 15 minutes of preparing the adjusted inoculums Application of E-test strips: Open E-test package by cutting package along the broken line. Apply strips to agar surface using forceps or E-test applicator if available.
If strips stick together, they may be pulled apart by handling the section marked E. Do not touch any other area of the strip. Use templates to position 4 to 6 strips onto a mm plate or one seldom two strips onto a 90 mm plate. Do not remove or replace a strip once it has touched the agar.
Repeat the entire procedure also for Quality control Strain E. Result and Interpretation: A Staphylococcus aureus isolate tested by the Etest gradient diffusion method Read MIC at the point where ellipse intersects the scale. If a MIC value between two twofold dilutions is seen, always round up to the highest value.
Read the MIC value at complete inhibition of all growth. If the intersect differs on either side of the strip, read the MIC as the greater value. Ignore any growth at the edge of the strip. Share this:.
Epsilometer test (E test)
Opening an E-test package 1. Equilibrate at room temperature. Ensure all the moisture has evaporated before opening. Inspect the package for holes or crack. Do not use if damaged. Do not cut between the blisters.
It is a cost-effective tool that has been developed to provide a direct quantification of antimicrobial susceptibility of microorganisms. It is a quantitative method that applies both the dilution of antibiotics and the diffusion of antibiotics into the medium. More precisely, the test combines a disk diffusion pattern with the determination of Minimum Inhibitory Concentration MIC which is considered as the lowest concentration of an antimicrobial that inhibits the visible growth of a microorganism. The E-test uses rectangular plastic strips with the predefined, continuous and exponential gradient of antibiotic concentration one side of the strip contains the antimicrobial agent concentration gradient and the other side of the strip contains a numeric scale that indicates the drug concentration. Objectives To determine the MIC of fastidious, slow-growing or nutritionally deficient micro-organisms.
E-TEST ( Epsilometer test): Principle, purpose, procedure, results and interpretations
During the s, Hans Ericsson Professor of microbiology at the Karolinska Hospital and Karolinska Institute, Stockholm , the scientific founder of AB BIODISK, developed a method to standardize the disc diffusion method and to improve its reproducibility and reliability for clinical susceptibility predictions. The inhibition zone sizes from disc test results were compared to Minimum Inhibitory Concentration MIC values based on the reference agar dilution procedure. The correlation between zone sizes and MIC values was then assessed using regression analysis and regression lines were used for extrapolating zone interpretive limits that corresponded to the MIC breakpoint values that defined susceptible, intermediate and resistant categorical results. Etest applications include many groups of fastidious organisms, fungi yeast and mould and mycobacteria as well as detecting various mechanisms of resistance and MIC testing of key antibiotics with critical specimens e. Next to bacteria it can also be used to determine the MIC for certain fungi. When Etest is applied to the surface of an agar plate inoculated with the test strain, there is an instantaneous release of the antimicrobial gradient from the plastic carrier to the agar to form a stable and continuous gradient beneath and in the immediate vicinity of the strip. Etest incubation and reading times have been determined based on the intrinsic growth characteristics of the organism, and the specific incubation conditions.