Epsilometer test

History

The principle of the epsilometer test was first described in 1988 and was introduced commercially in 1991 by AB Biodisk.

Principle

The Etest is basically an agar diffusion method.

The Etest utilises a rectangular strip that has been impregnated with the drug to be studied. A lawn of bacteria is inoculated onto the surface an agar plate and the Etest strip is laid on top; the drug diffuses out into the agar, producing an exponential gradient of the drug to be tested. There is an exponential scale printed on the strip. After 24 hours of incubation, an elliptical zone of inhibition is produced and the point at which the ellipse meets the strip gives a reading for the minimum inhibitory concentration (MIC) of the drug.

Validation

The test has been validated for many organisms against the broth/agar dilution method and shown to have excellent correlation. This is a partial list of organisms and antibiotics for which the test has been validated.

Pseudomonas aeruginosa: amikacin, ceftazidime, gentamicin, piperacillin, ticarcillin, tobramycin,

The following list (in alphabetical order) reflects Etest strips available in the United States for in vitro diagnostic use (as of Jan 2010): Amikacin, Amoxi/clav, Amoxicillin, Ampicil/sulb, Ampicillin, Azithromycin, Aztreonam, Benzylpenicillin (32 and 256ug/ml), Cefaclor, Cefepime, Cefotaxime (32 and 256ug/mL), Cefotetan, Cefoxotin, Ceftazadime, Ceftizoxime, Ceftriaxone, Cefuroxime, Cephalothin, Chloramphenicol, Ciprofloxacin, Clindamycin, Daptomycin, Doripenem, Ertapenem, Erythromycin, Fosfomycin, Gatifloxacin, Gemifloxacin, Gentamicin (256 and 1024ug/mL), Imipenem, Levofloxacin, Linezolid, Meropenem, Metronidazole, Minocycline, Moxifloxacin, Ofloxacin, Oxacillin, Pip/Tazo, Piperacillin, Quinupri/Dalfopri, Rifampicin, Ticar/Clav, Tigecycline, Trim/Sulfa, Trimethoprim, Vancomycin,

Etest for Antifungal Susceptibility Testing

Fluconazole, Itraconazole, Flucytosine, Voriconazole

Etest for Extended spectrum beta-lactamase Detection

Cefotaxime/Clav. acid, Ceftazidime/Clav. acid

References

^ Joyce LF, Downes J, Stockman K, Andrew JH (1 October 1992). “Comparison of five methods, including the PDM Epsilometer test (E test), for antimicrobial susceptibility testing of Pseudomonas aeruginosa”. Journal of Clinical Microbiology 30 (10): 27092713. PMID 1400972. PMC 270503. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=270503. 

External links

Mendoza MT (1998). “What New in Antimicrobial Susceptibility Testing?”. Phil J Microbiol Infect Dis 27 (3): 113115. 

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