Evaluation of the compatibility of EUCAST Direct Rapid Antimicrobial Susceptibility Test (RAST) Method Results with Automated Systems in Positive-Signaling Blood Culture Bottles

Abstract

The aim of this study is to compare the RAST results with the Vitek 2 automatic system and evaluate its effectiveness. Total of 76 strains, including anonymous 15 Pseudomonas aeruginosa, 24 Escherciae coli, 16 Klebsiella pneumoniae, 6 Staphylococcus aureus, 11 Enterococcus faecalis, 1 Streptococcus pneumoniae, 3 Acinetobacter baumanii, found in the laboratory culture collection was included in the study. Rapid Antimicrobial Susceptibility Test (RAST) was performed in accordance with European Committee on Antimicrobial Susceptibility Testing (EUCAST) recommendations. A 10 µg ceftazidime disk was used for the detection of Extended Spectrum Beta-Lactamase (ESBL) by the RAST method. After incubation, it was interpreted as susceptible (S), resistant (R) and technical uncertainty area (ATU) according to EUCAST RAST v.1.1 breakpoint tables. Categorical results in 4, 6, 8 and 20 hours incubation were compared with vitek 2 automated system results. 581 disc diffusion studies were performed for all strains. Measurable zone diameter of inhibition occurred in 444 (76.4%) disc studies. The agreement between the results of the studies evaluated as sensitive and resistant by RAST with the results of the Vitek 2 automated system was found to be 98.4%. Compatibility with Vitek 2 automated system at the fourth hour was 98.1%; it was 97.9% at the sixth hour and 100% at the eighth hour. Our study shows that the RAST results are quite compatible with the conventional method. Therefore, although there are difficulties in routine laboratory practice, the results obtained with RAST show that it will provide rapid evaluation of empirical antibiotic therapy in bloodstream infections.