DETERMINATION OF STABILITY CHARACTERISTICS OF PSEUDOMONAS AERUGINOSA STRAINS USED IN AN EXTERNAL QUALITY ASSESSMENT PANEL

Abstract

To study the stability characteristics of Pseudomonas aeruginosa for the development of an external quality assessment (EQA) panel. Materials and Methods: The study was conducted during 2023–2025 in the reference laboratory of the Antimicrobial Resistance Center of the RSSPMCEMIPD. A total of 29 P. aeruginosa strains and one control strain — Pseudomonas aeruginosa NCTC 12934 — were included in the study. Identification was performed using conventional methods and the BD Phoenix (USA) automated system. Antimicrobial susceptibility testing and determination of minimum inhibitory concentrations (MICs) were carried out.To assess strain stability, two preservation methods were evaluated: storage at ultra-low temperature (–80 °C) and lyophilization. Under –80 °C storage conditions, testing was performed four times, and after lyophilization, three times.Results: Using the disk diffusion method, the coefficient of variation (CV) did not exceed 10% for AK30, CN10, CIP5, and LEV5. For IMI10 and MRP10, slight fluctuations in mean inhibition zone diameters were observed at 12 months; however, CV values remained within acceptable limits. For FEP30, CV reached 13–14%, but the mean values and 95% confidence intervals remained comparable across storage periods.Analysis of MIC measurements demonstrated stability of minimum inhibitory concentrations for AK30, CN10, LEV5, FEP30, and CAZ10 throughout all storage durations.Conclusion: The study of P. aeruginosa strain stability showed that not all strains retain their characteristics during storage. According to our results, 6 strains of P. aeruginosa (21%) maintained their properties and were selected for the formation of the EQA panel.