Evaluation of Resistance in Staphylococcus aureus Strains Isolated From Blood Cultures to Methicillin and Other Antimicrobial Agents

Objective: Evaluation of the frequency and antimicrobial susceptibility of organisms isolated from blood cultures, leads clinicians to start an empirical treatment. Staphylococcus aureus has an important place among organisms isolated from bloodstream infections. Antibiotic resistance in these organisms causes serious problems in the treatment of infections. In this study, we aimed to investigate antimicrobial susceptibility of S. aureus strains isolated from bloodstream infections and to contribute to the antibiotic policy in the hospital. Methods: In our study, antibiotic resistance of S. aureus strains isolated from blood cultures of inpatients were investigated retrospectively. Blood cultures were performed with BacT/Alert (R) 3D (bioMerieux, Marcy l'Etoile, France) between August 2017 and August 2018, and in Render BC128 (Shandong Huifa Electronics Technology Co., Jinan, Shandong, China) automated blood culture systems between August 2018 and August 2019. Bacterial identification was performed using conventional methods and BD Phoenix (TM) 100 (Becton Dickinson Co., Sparks, Maryland, USA) automated identification system. Antimicrobial susceptibility tests of bacteria were performed with the same automated system taking into consideration the recommendations of the European Committee on Antimicrobial Susceptibility Testing. Results: During the two years period, 20 367 blood culture samples were examined, and culture positivity was observed in 22.1%. Of 390 (8.6%) S. aureus strains, 160 (41.02%) were identified as methicillin-resistant (MRSA) and 230 (8.98%) were identified as methicillin-sensitive (MSSA). There was no resistance against vancomycin, teicoplanin, daptomycin, linezolid, and quinupristin-dalfopristin. No resistance to trimethoprim-sulfamethoxazole (SXT) was detected in MSSA strains. Clindamycin, aminoglycosides and fusidic acid were also highly active against these strains, while other antibiotics were found to have resistance rates ranging from 10% to 57%. While the SXT resistance rate to MRSA strains was 3.1%, the resistance rates of the other antibiotics tested ranged from 43% to 91%. Conclusions: Uncontrolled use of antibiotics increases the development of resistance. High resistance was found to all antimicrobials in MRSA isolates and to fluoroquinolones in all S. aureus isolates. These show that antibiotic policy should be reviewed, awareness of rational antibiotic use should be established, and restricted use of some antibiotics should be implemented in the hospital.