Developing a Simple, Applicable, and Reliable Method to Produce and Standardize an Epsilometer (Etest) Strip for Antimicrobial Susceptibility and Minimum Inhibitory Concentration Evaluations

Montaseri, Hashem; Khajeh, Fatemeh; Sobhani, Zahra; Akbarizade, Amin Reza; Faraz, Marzieh

doi:10.30476/tips.2026.110209.1346

Developing a Simple, Applicable, and Reliable Method to Produce and Standardize an Epsilometer (Etest) Strip for Antimicrobial Susceptibility and Minimum Inhibitory Concentration Evaluations

Document Type : Original Article

Authors

¹ department of Quality Control, Shiraz Faculty of Pharmacy, Shiraz University of medical Sciences, Shiraz, Fars. IR

² Department of Pharmaceutical Quality Control, Faculty of Pharmacy, Shiraz University of Medical Sciences, Shiraz, Iran

10.30476/tips.2026.110209.1346

Abstract

Microbial infections remain a major global health and economic burden due to increased morbidity, mortality, prolonged hospitalization, and rising antimicrobial resistance. Rapid and accurate minimum inhibitory concentration (MIC) determination is essential for effective antibiotic therapy and resistance prevention. Conventional methods, including broth micro- and macrodilution, disk diffusion, and agar well diffusion, are limited by long turnaround times, high costs, and poor quantitative precision.
The Etest strip method overcomes these limitations by creating a precise antibiotic gradient on agar, delivering accurate MIC readings within 16–24 hours. However, developing countries like Iran rely entirely on imported Etest strips, facing challenges such as high costs, sanctions, currency fluctuations, and inconsistent supply.
This study developed a simple, cost-effective domestic production method for Etest-like strips suitable for water-soluble antibiotics. Cellulose-based substrates with uniform weight and solvent absorption (K2) and a safe, locally available inert adhesive (G1) were used. Ciprofloxacin served as the model antibiotic, with Escherichia coli as the test organism. Drug loading and release were quantified via validated UV-Vis spectrophotometry (λ_max = 270 nm, R² = 0.9998, accuracy 97.21%, precision <3%).
Prototype strips exhibited stable drug release after 20 minutes and consistent performance. MIC readings from prepared strips were compared and calibrated against CLSI-standard methods, yielding clinically equivalent results. Strips remained stable for at least 2 months at 25 ± 2 °C and 2–8 °C.
This platform enables manual scaling, supports import substitution, accelerates susceptibility testing, and enhances antimicrobial stewardship in resource-limited settings.

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