Etest

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Etest being used to determine the susceptibility of Neisseria gonorrhoeae to benzylpenicillin. E-test Ngono.jpg
Etest being used to determine the susceptibility of Neisseria gonorrhoeae to benzylpenicillin.

Etest (previously known as the Epsilometer test) is a way of determining antimicrobial sensitivity by placing a strip impregnated with antimicrobials onto an agar plate. A strain of bacterium or fungus will not grow near a concentration of antibiotic or antifungal if it is sensitive. For some microbial and antimicrobial combinations, the results can be used to determine a minimum inhibitory concentration (MIC). Etest is a proprietary system manufactured by bioMérieux. It is a laboratory test used in healthcare settings to help guide physicians by indicating what concentration of antimicrobial could successfully be used to treat patients' infections. [1]

Contents

Use

Etest is a quantitative technique for determining the MIC of microoganisms. It is used for a range of Gram-negative and Gram-positive bacteria such as Pseudomonas , [2] [3] Staphylococcus , [4] and Enterococcus species, [5] as well as fastidious bacteria, such as Neisseria and Streptococcus pneumoniae . [1] It can also be used to determine MICs against certain fungi. [6] [7]

Etest is a pre-prepared non-porous plastic reagent strip with a predefined gradient of antibiotic, covering a continuous concentration range. [8] It is applied to the surface of an agar plate inoculated with the test strain, where there is release of the antimicrobial gradient from the plastic carrier to the agar to form a stable and continuous gradient beneath and in nearby to the strip.

The time taken for a plate to be ready depends on the m that is being tested, and the conditions of the agar plate.[ citation needed ] The predefined Etest gradient remains stable for at least 18 to 24 hours; that is, a period that covers the critical times of many species of fastidious and non-fastidious organisms.

After the test, the bacterial growth becomes visible after incubation and a symmetrical inhibition ellipse centered along the strip is seen. The MIC value is read from the scale in terms of μg/mL where the ellipse edge intersects the strip. After the required incubation period, the minimum inhibitory value is read where the edge of the inhibition ellipse intersects the side of the strip. The plate should not be read if the culture appears mixed or if the lawn of growth is too light or too heavy.[ citation needed ]

Etest MIC endpoints are usually clear-cut although different growth/inhibition patterns may be seen depending on the antifungal or antibiotic used. [7]

E-test being used to determine the susceptibility of Candida albicans to caspofungin. E-test Caspofungin.jpg
E-test being used to determine the susceptibility of Candida albicans to caspofungin.

Selection of agar medium

Etest can be used with many different kinds of AST agar medium as long as the medium supports good growth of the test organism and does not interfere with the activity of the antimicrobial agent. However, to maximise reproducibility, the medium chosen should fulfil the basic requirements for a susceptibility test medium. The following AST media are recommended for use with Etest:[ citation needed ]

These media may require supplemental nutrients to obtain enhanced growth of nutritionally fastidious organisms such as pneumococci, streptococci, Abiotrophia, Haemophilus, gonococci, meningococci and Campylobacter. In general, media recommendations from the Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) are considered appropriate for Etest.

Etest equipment

The Etest family of instruments is designed to simplify the daily use of Etest. Simplex C76, Nema C88, and Retro C80 are easy to use, reducing operator fatigue, saving time and improving the quality of results by increasing reproducibility. Etest and related instruments offer one of the most efficient methods for generating on-scale MIC values across 15 doubling dilutions for susceptibility testing of a wide range of drug-bug combinations, including fastidious organisms.

History

The Etest strip was first described in 1988 and was introduced commercially in 1991 by AB BIODISK. [5] bioMérieux acquired AB BIODISK in 2008 and continues to manufacture and market this product range under the mark Etest.

During the 1950s, 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 disk diffusion test and to improve its reproducibility and reliability for clinical susceptibility predictions.[ citation needed ] The inhibition zone sizes from disk test results were compared to 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 was first presented at the Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) in Los Angeles in 1988 as a novel gradient concept for MIC determinations. In September 1991, Etest was launched globally as a MIC product after receiving the USA Food and Drug Administration (FDA) clearance.[ citation needed ]

See also

References

  1. 1 2 bioMérieux. "ETEST®". www.biomerieux-usa.com. bioMérieux. Retrieved March 18, 2021.
  2. Joyce, L F; Downes, J; Stockman, K; Andrew, J H (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): 2709–2713. doi:10.1128/JCM.30.10.2709-2713.1992. PMC   270503 . PMID   1400972.
  3. Morosini, María I.; García-Castillo, María; Loza, Elena; Pérez-Vázquez, María; Baquero, Fernando; Cantón, Rafael (September 2005). "Breakpoints for Predicting Pseudomonas aeruginosa Susceptibility to Inhaled Tobramycin in Cystic Fibrosis Patients: Use of High-Range Etest Strips". Journal of Clinical Microbiology. 43 (9): 4480–4485. doi:10.1128/JCM.43.9.4480-4485.2005. PMC   1234086 . PMID   16145095.
  4. Cantón R, Livermore DM, Morosini MI, Díaz-Regañón J, Rossolini GM, et al. (February 2017). "Etest® versus broth microdilution for ceftaroline MIC determination with Staphylococcus aureus: results from PREMIUM, a European multicentre study". Journal of Antimicrobial Chemotherapy. 72 (2): 431–436. doi: 10.1093/jac/dkw442 . hdl: 10447/417933 . PMID   27798220.
  5. 1 2 Khan, Zeeshan A.; Siddiqui, Mohd F.; Park, Seungkyung (3 May 2019). "Current and Emerging Methods of Antibiotic Susceptibility Testing". Diagnostics. 9 (2): 49. doi: 10.3390/diagnostics9020049 . PMC   6627445 .
  6. Chang, Hsein Chang; Chang, Jui Jung; Chan, Shih Huang; Huang, Ay Huey; Wu, Tsu Lan; Lin, Miao Chu; Chang, Tsung Chain (April 2001). "Evaluation of Etest for direct antifungal susceptibility testing of yeasts in positive blood cultures". Journal of Clinical Microbiology. 39 (4): 1328–1333. doi:10.1128/JCM.39.4.1328-1333.2001. ISSN   0095-1137. PMC   87934 . PMID   11283051.
  7. 1 2 "Antifungal susceptibility testing" (PDF). www.biomerieux-industry.com/. bioMérieux. February 2013. Retrieved March 15, 2021.
  8. Ge, Beilei; Wang, Fei; Sjölund-Karlsson, Maria; McDermott, Patrick F. (October 2013). "Antimicrobial resistance in Campylobacter: Susceptibility testing methods and resistance trends". Journal of Microbiological Methods. 95 (1): 61. doi:10.1016/j.mimet.2013.06.021.