1Ahi Evran University, Medical School, Department of Medical Microbiology, Kirsehir, Turkey - 2Ahi Evran University, Training and Research Hospital, Microbiology Laboratory, Kirsehir, Turkey 


Introduction: The European Committee on Antimicrobial Susceptibility Testing (EUCAST) is a standard used for the implemen- tation and evaluation of antibiotic susceptibility tests in many European countries. The EUCAST standard has been used in Turkey since 2015. The aim of this study is to evaluate the differences in antibiotic susceptibilities of Pseudomonas aeruginosa (P. aeruginosa) isolates using local data during the transition process from the Clinical Laboratory Standards Institute (CLSI) standards to EUCAST.

Materials and methods: In total, 105 non-duplicate clinical isolates of P. aeruginosa were analyzed. Conventional methods and the Vitek-2 automated system (bioMérieux, France) were used to identify the isolates. Antibiotic susceptibility tests were performed with the Kirby-Bauer disc diffusion method. In addition to the routinely used discs, ceftazidime 10 μg and piperacillin/tazobactam 30/6 μg were added to create different contents for both of the standards. The antibiotic susceptibility zone diameters of the isolates were evaluated in accordance with the CLSI 2014 and EUCAST 2014 standards, and a difference in the ratio of resistance levels was found.

Results: It was observed that antibiotics with different disc contents had different resistance ratios according to the evaluation made with each of the standards. The resistance ratio of ceftazidime (10μg to 30μg) and piperacillin/tazobactam (100/10 μg to 30/6 μg ) in P.aeruginosa increased from 1.9% and 0.95% to 4.8% and 15.2%, respectively, when we compared the CLSI 2014 with the EUCA- ST 2014 standards. There were no significant differences in the susceptibility results for imipenem, meropenem, amikacin, gentamicin, ciprofloxacin, levofloxacin, and cefepime.

Conclusion: Antimicrobial susceptibility testing is one of the most important tasks in clinical microbiology laboratories. Upon the implementation of the EUCAST guidelines, laboratories should be aware of the implications of modified drug susceptibility testing reports on antibiotic prescription policies. Additionally, the continuity of local surveillance activities should be ensured. 


Pseudomonas aeruginosa, antimicrobial susceptibility tests, Clinical Laboratory Standards Institute (CLSI), European Committee on Antimicrobial Susceptibility Testing (EUCAST).