Implementation of the EUCAST rapid antimicrobial susceptibility test (RAST) directly from positive blood culture bottles without the advanced identification systems

Objectives EUCAST published its recommendations for rapid antimicrobial susceptibility tests (RASTs) directly from positive signal blood culture (BC) bottles. The objective of the present study was to investigate the accuracy and applicability of the predicted RAST (p-RAST) method without using automated identification systems, and the effects of the results obtained with this method on the treatment decision of the clinician. Methods The RAST procedure was applied to positive BC samples between November 2020 and June 2021. The categorical results of the method were obtained by comparing the p-RAST results obtained at 4, 6 and 8 h of incubation according to predicted bacterial species with conventional methods and standard disc diffusion results. The effects of these results on the treatment decision of the clinician were evaluated retrospectively. The actual categorical results of the EUCAST RAST [standard RAST (s-RAST)] method were identified. Results The p-RAST and s-RAST results were analysed according to 145 and 111 isolates, respectively. The p-RAST total error rates were 3.0%, 3.1% and 2.8% at 4, 6 and 8 h of incubation, respectively, and the s-RAST total error rates were determined as 2.7%, 3.3% and 3.2%, respectively. With p-RAST's results, it was observed that effective escalation was performed in the antimicrobial treatment for 45 patients, and effective de-escalation could be performed in 32 patients, but it was recommended not to perform de-escalation. Conclusions Even in a microbiology laboratory with limited facilities, reliable antimicrobial susceptibility test results can be obtained in a short time with the p-RAST method without using automated systems and antimicrobial choice can be guided in a shorter time.