E test

E Test

The E Test or Epsilometer test is a method used to determine the antibiotic sensitivity or resistance of bacteria. It is a type of agar diffusion test, and is also known as the gradient diffusion method.

Overview

The E Test is a quantitative method for determining the Minimum Inhibitory Concentration (MIC) of antibiotics, antifungal agents, and antimycobacterial agents. The test is named for the "E" shaped strip that contains a gradient of antibiotic concentrations. The strip is placed on an agar plate that has been inoculated with the test organism, and the MIC is read where the elliptical zone of inhibition intersects the strip.

Procedure

The E Test procedure involves several steps:

1. A pure culture of the test organism is prepared in a suitable broth medium.
2. The culture is swabbed onto the surface of an agar plate.
3. An E Test strip is placed on the agar surface.
4. The plate is incubated at the appropriate temperature and for the appropriate time.
5. The MIC is read at the point where the zone of inhibition intersects the strip.

Interpretation

The interpretation of E Test results is based on established criteria for the specific antibiotic and organism being tested. The MIC is the lowest concentration of the antibiotic that inhibits the growth of the organism. If the organism grows up to the edge of the E Test strip, it is considered resistant to the antibiotic. If there is a zone of inhibition around the strip, the organism is considered sensitive to the antibiotic.

Advantages and Limitations

The E Test has several advantages over other methods of antibiotic susceptibility testing. It provides a direct quantitation of antimicrobial susceptibility, and it can be used with a wide range of organisms and antimicrobial agents. However, the E Test also has some limitations. It is more expensive than other methods, and it requires a higher level of technical skill to perform and interpret.

See also

• Antibiotic susceptibility test
• Disk diffusion test
• Broth dilution test

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