Objective: Nosocomial Pseudomonas aeruginosa infections are accepted a serious healthcare problem with a high morbidity and mortality rates. Therapeutic options are restricted increasingly due to the development of resistance. The purpose of this study was to compare the antimicrobial resistance status of 250 nosocomial Pseudomonas aeruginosa isolates from our hospital according to EUCAST-2022 and CLSI-2022 breakpoints and also evaluate the presence of metallo-beta-lactamase (MBL) activity by different phenotypic methods.

Methods: Antibiotic susceptibility testing of 250 nosocomial P. aeruginosa isolates were performed using disc diffusion method. The results were evaluated according to EUCAST (The European Committee on Antimicrobial Susceptibility Testing) and CLSI (Clinical Laboratory Standards Institute) criteria. MBL production of carbapenem resistant isolates were screened by double disk synergy test, combined disk diffusion test and modified hodge test.

Results: In our study, nosocomial P. aeruginosa isolates were most frequently isolated from respiratory tract samples, followed by urine samples. Among the tested antibiotics, nosocomial P. aeruginosa isolates were most sensitive to ceftazidime-avibactam (96%) according to EUCAST-2022 criteria, and ceftolozane-tazobactam (95.2%) according to CLSI-2022 criteria. When the susceptibility profiles of P. aeruginosa isolates were compared according to EUCAST and CLSI criteria; the higher resistance rates for ciprofloxacin, levofloxacin, ticarcillin-clavulanic acid, cefepime, aztreonam, imipenem and doripenem were observed according to EUCAST-2022 criteria. In contrast amikacin resistance rate was found to be lower according to CLSI-2022 criteria. MDR (98%) determined according to EUCAST-2022 criteria was found to be higher than MDR determined according to CLSI-2022 criteria (36%). MBL positivity was found to be 36.8% with the combined disc diffusion test, 38.2% with the double disc synergy test and 36.8% with the modified Hodge test. In terms of MBL production, we didn’t observe any statistical significance between the phenotypic methods.

Conclusion: When evaluated according to EUCAST-2022 criteria, resistance rates of ciprofloxacin, levofloxacin, ticarcillin-clavulanic acid, cefepime, aztreonam, imipenem and doripenem are higher in nosocomial P. aeruginosa isolates. Increased MBL production and multi drug resistance in nosocomial P. aeruginosa isolates result in significant limitation of treatment options. Besides the antimicrobial susceptibility testing, phenotypic MBL screening methods must be performed for the selection of the appropriate antimicrobial therapy and for the close monitoring the development and spread of resistance.